Diboron(4) Compounds: From Structural Curiosity to Synthetic

This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.

Review pubs.acs.org/CR

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse Emily C. Neeve,† Stephen J. Geier,§ Ibraheem A. I. Mkhalid,‡ Stephen A. Westcott,*,§ and Todd B. Marder*,† †

Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Würzburg 97074, Germany Mount Allison University, Department of Biochemistry and Chemistry, Sackville, New Brunswick E4L 1G8, Canada ‡ Department of Chemistry, King Abdulaziz University, Jeddah 21413, Saudi Arabia §

ABSTRACT: Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B−C bonds and other processes.

CONTENTS 1. Introduction 2. Synthesis, Structure, and Bonding of Diboron(4) Compounds 2.1. B2X4 Compounds 2.2. B2H4 Chemistry 2.3. B2(NR2)4 Compounds 2.4. B2(alkyl)n Compounds 2.5. B2(OR)4 Compounds 2.5.1. Synthesis of B2(OR)4 2.5.2. Adducts of B2(OR)4 Compounds 2.6. Three-Membered Aromatic Heterocycles Containing B−B Bonds 2.7. Diboryl Groups as Ligands 2.8. [2]-Borametalloarenophanes 2.9. B−B Bonding 3. 1,2- and 1,4-Diborations 3.1. Mechanistic Studies of 1,2-Diboration Processes 3.2. Alkynes 3.3. Alkenes (Aliphatic) 3.4. Alkenes (Vinyl Arenes) 3.5. Alkenyl and Alkynyl Boronate Esters 3.6. Dienes 3.7. Allenes 3.8. Carbonyls and Thiocarbonyls 3.9. Imines 3.10. Other Substrates 3.11. Unsaturated Carbonyls 3.12. Diagram Summarizing Section 3 © XXXX American Chemical Society

4. Boryl Addition (Hydroboration) Reactions 4.1. α,β-Unsaturated Carbonyls, Imines, and Related Compounds 4.2. Alkynes 4.3. Alkenes 4.4. Dienes, Enynes, and Allenes 4.5. Aldehydes and Imines 4.6. Ring-Opening Reactions 4.7. Borylative Cyclizations and Related Intermolecular Reactions 4.8. Boron-Element Additions Across Mutiple Bonds 4.9. Diagram Summarizing Section 4 5. Boryl Substitutions 5.1. Coupling Reactions 5.2. Allylic and Propargylic Substitutions 5.3. Alkyl Substitutions 5.4. Alkenyl Substitutions 5.5. Aromatic Substitutions 5.5.1. Aryl Halides 5.5.2. Aryl C−O Electrophiles 5.5.3. Aryl C−N Bonds 5.5.4. Aryl Nitriles 5.6. Diagram Summarizing Section 5 6. Conclusion Author Information Corresponding Authors

B C C D D E E E F H H H I K K N O Q R S T V W W X Y

Y Y AC AE AF AG AG AH AI AJ AJ AJ AK AN AO AO AO AS AT AT AU AU AU AU

Received: March 22, 2016

A

DOI: 10.1021/acs.chemrev.6b00193 Chem. Rev. XXXX, XXX, XXX−XXX

Chemical Reviews

Review

Figure 1. Diboron compounds.

Notes Biographies Acknowledgments References

1b).11 This compound was arduously prepared by the slow passage of B5H9, in an atmosphere of dihydrogen, through an electric discharge between copper electrodes. Not surprisingly, while several theoretical and physical studies have focused on this complex,12−22 its complicated synthesis has limited the synthetic potential of this unique diboron compound, and its chemistry remains largely unexplored. A different structural isomer of B10H16, also bearing a central B−B bond where neither boron atom bears a terminal hydride, was prepared by Sneddon and co-workers through the dehydrocoupling of B5H9.23 Brown further extended research on diboron compounds by developing a pantheon of alkyl- and dialkylboranes by the addition of BH3·LB (where LB = Lewis base, such as THF or SMe2) to alkenes. For example, the addition of borane to cyclooctadiene affords 9-borabicyclo[3.3.1]nonane (9-BBN, Figure 1c),24 which has found extensive use in hydroboration reactions, wherein the B−H bond of the borane adds to an unsaturated organic fragment to generate the corresponding organoborane. In the absence of a Lewis base, dialkylboranes usually exist as dimers, in which the two boron fragments are once again connected by two three-center, two-electron B−H− B bridges. In 2010, the Nobel Prize was awarded to Professor Akira Suzuki for his outstanding work on cross-coupling reactions and the corresponding organoborane products and boronate reagents that have all but usurped the role of their more toxic tin counterparts.5,25 The Suzuki−Miyaura reaction uses organoboranes (primarily aryl boronic acids, ArB(OH)2, and their boronate ester derivatives, ArB(OR)2) and organic halides (ArX or RX), in the presence of a catalyst, to generate organic products containing a new C−C bond (Scheme 1a and 1b). Although aryl boronic acid derivatives have traditionally been prepared using Grignard and organolithium reagents, alternative borylation reactions using dialkoxyboranes or diboron(4) compounds, such as B2cat226 (cat = 1,2-O2C6H4), B2pin227,28 (pin =1,2-O2C2Me4, Figure 1d), and B2neop229 (neop = OCH2CMe2CH2O, Figure 1e), have been developed (Scheme 1c). These diboron(4) compounds are relatively stable and easy to handle and are increasingly utilized in all aspects of chemistry. Indeed, it is now difficult to keep pace with the latest developments using these tetraalkoxydiboron(4) compounds, including tetrahydroxydiboron, as their full potential is still coming to light (Figure 2).30−56 The volume of papers published in this area has grown exponentially, with bis(pinacolato)diboron appearing as a reactant or reagent in as many as 8193 publications (SciFinder, 01.02.2016). The utility of these remarkable compounds continues to grow rapidly,

AU AU AV AV

1. INTRODUCTION The advent of diboron(4) compounds in 1925 introduced a new group of reagents that would eventually prove to be very versatile and extremely useful in many synthetic pathways to form a range of valuable natural products, pharmaceutical intermediates, and biologically active compounds.1 Furthermore, organic compounds containing boron are ideal candidates for green chemistry as they are generally considered nontoxic to plants, mammals, and other complex life forms and are therefore environmentally benign.2 The past few decades have seen remarkable progress in both inorganic and organic boron chemistry, with several people awarded the Nobel Prize for their ground-breaking research in these emerging areas.3−5 William Lipscomb and Herbert Brown were awarded the Nobel Prize in 1976 and 1979, respectively, for their contributions to the field of boron chemistry. Lipscomb’s main contribution in this field came from deducing the nature of chemical bonding in boranes, such as B2H6, diborane(6), and clusters (Figure 1a), although he also made significant contributions to both nuclear magnetic resonance spectroscopy and in the chemistry of large biomolecules. Using X-ray crystallography as a method of structural determination, Lipscomb and others6−9 were able to assess the nature of B2H6, where the two “BH3” fragments were connected to one another through two B−H−B interactions with a pair of electrons shared among the three atoms. No significant boron− boron interaction is believed to occur in these three-center twoelectron bonds, and the chemistry of diborane(6) proceeds primarily via cleavage, either homolytically or heterolytically, of the two B−H−B bonds. Furthering the understanding of boron chemistry, Nobel Prize laureate Roald Hoffmann was a doctoral student in Lipscomb’s laboratory and later responsible, in part, for developing the extended Hückel method for calculating molecular orbitals, the fragment molecular orbital (FMO) approach, and for developing the isolobal analogy well beyond the boron cluster field.10 Other notable boron chemists that worked with Lipscomb included M. Frederick Hawthorne, pioneer in the synthesis of boron and carborane clusters and their metal-containing compounds, and Russell Grimes, who found that a remarkable boron hydride, namely, B10H16, contains a direct and unsupported B−B bond, where neither of the central boron atoms has a terminal hydride (Figure B


Chemical Reviews

Review

preparation of B2Cl4 have been examined,63−70 including an early reaction using microwave excitation of gaseous boron trichloride,71 these attempts suffered from low yields and harsh reaction conditions. Interestingly, diboron tetrachloride has been prepared by reaction of boron trichloride with boron monoxide, x(BO)x, at 200 °C.72 The starting boron monoxide was generated by dehydration of tetrahydroxydiboron(4), B2(OH)4, previously prepared by the hydrolysis of tetrakis(dimethylamino)diboron(4), B2(NMe2)4, in aqueous hydrochloric acid solution. Furthermore, Schlesinger et al. investigated the reaction of B2Cl4 with BBr3 to obtain the first proof for the formation of B2Br4.63 However, later, the diboron tetrabromide species was prepared using a similar methodology to the B2Cl4 system with tetramethoxydiboron(4) and boron tribromide.68,73 The importance of these tetrahydroxy-, tetramethoxy-, and tetraaminodiboron(4) compounds will be addressed later (sections 2.3 and 2.5). Investigations into the synthesis of related diboron tetrahalides, B2I4 and B2F4, were also conducted. The preparation of diboron tetraiodide was first reported by Schumb in 1949 using electrodeless radiofrequency discharge to reduce BI3,74,75 while B2F4 was initially prepared, almost a decade later, in 1958 from the reaction of B2Cl4 and SbF3.76 In 1967, Timms reported the formation of B2F4, as well as triboron pentafluoride, during the co-condensation of BF with BF3 at −196 °C.77 Furthermore, several years later, he also showed that a similar system could be used to synthesize B2Cl4.66,69,78 While the existence of homoatomic bonds was well known for carbon, nitrogen, and oxygen, the possibility that an electropositive element such as boron could form an unsupported bond with itself gave birth to a whole new area of chemistry. Early studies on the structure79 and reactivity75,80−86 of boron subhalides found that these species behaved as bifunctional Lewis acids. For example, addition of PCl3 to B2Cl4 gave the adduct (PCl3)2·B2Cl4 as the major boroncontaining species.81 However, more interestingly, the first diboration of ethylene using B2Cl4 was reported by Schlesinger et al. in 1954.80 The stereochemistry of this reaction was found to be specific for cis addition and consistent with a fourcentered transition state (Scheme 2).82 While this remarkable

Scheme 1. (a) Generic Suzuki−Miyaura Cross-Coupling Reaction; (b) Cross-Coupling of a Diborated Alkene with Iodobenzene; (c) Miyaura Borylation of an Aryl Halide with B2pin2

Figure 2. Number of publications featuring bis(pinacolato)diboron as a reactant or reagent per year.

warranting this new review which details many of the recent developments in this evolving area. However, due to the scale of papers published in this field, this paper will not include catalytic C−H borylation, for which there are already several excellent reviews focusing specifically on this area.51,57−60

2. SYNTHESIS, STRUCTURE, AND BONDING OF DIBORON(4) COMPOUNDS Compounds such as B2pin2 and B2neop2 (Figure 1) are referred to by some as diboron(4) and by others as diborane(4) species. The IUPAC nomenclature for such compounds also derives from their ring sizes, such that the correct name for bis(pinacolato)diboron, B2pin2, is 4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bi-(1,3,2-dioxaborolane), whereas for bis(neopentyl glycolato)diboron, B2neop2, the correct name is 5,5,5′,5′tetramethyl-2,2′-bi-(1,3,2-dioxaborinane). We employ the simple and widely used abbreviations and the general term diboron(4) for such compounds throughout the review.

Scheme 2. Diboration Reaction of Ethylene Using B2Cl4

reaction was later expanded to include B2F4 along with a family of unsaturated hydrocarbons, including vinyl halides, butadiene, and acetylene, the synthetic utility of this methodology was once again limited by the difficult and harsh reaction conditions necessary to produce the starting diboron(4) compounds.83 Recently, Fernández, and Brown conducted a DFT study, revisiting the reactions of B2X4 (X = Cl, Br, and F) with various unsaturated hydrocarbons, such as ethene or benzene, in the absence of a transition metal.87 The calculations showed that the addition of B2Cl4 to alkenes is extremely plausible and lower in energy than the alternative B2X4 additions, apart from B2Br4. Furthermore, it was reported that reactions of B2Cl4 with naphthalene and C 60 were easily accessible, and B 2 X 4

2.1. B2X4 Compounds

The genesis of diboron(4) compounds occurred in 1925 when Stock, Brandt, and Fischer prepared the first so-called boron subhalide, B2Cl4, by striking an arc across zinc electrodes immersed in liquid boron trichloride.1 Diboron tetrachloride was initially prepared in about 1% yield and in low purity (less than 90%) and found to react violently with moisture or oxygen. Conducting the reaction in the vapor phase using a mercury arc improved the yield considerably.61,62 Although numerous efforts to find more efficient methods for the C


Chemical Reviews

Review

compounds could undergo 1,4-addition to dienes, especially cyclopentadiene in the case of B2F4.87

Scheme 3. Formation of a Dinuclear Cobalt Complex Containing a Nonsubstituted Borylene Fragment108

2.2. B2H4 Chemistry

After the discovery of the stable D2d and D2h forms of subhalides, there was considerable interest in the parent B2H4 compound. Mohr and Lipscomb used computational studies to suggest that the D2d form is more stable than the other forms (Figure 3), including the nonplanar doubly bridged structure by

group 9 metals are thought to be regarded as early stage oxidative addition of the boron−boron bond, leading to diboryl compounds.121 Metal complexes derived from addition of basestabilized diboron(4) compound have been studied from a structural standpoint, but their reactivity with organic molecules has yet to be investigated. Interestingly, in a recent computational study, Jemmis and co-workers analyzed the interaction between transition-metal complexes and B2H4 as a ligand.122 A unique case study for the Dewar−Chatt−Duncanson model was proposed, in which B2H4 could be stabilized by formation of transition-metal π-complexes such as [Cr(CO)4B2H4], [Mn(CO)CpB2H4], [Fe(CO)3B2H4], and [CoCpB2H4].122

Figure 3. Potential geometries for B2H4.

only 1.5 kcal/mol.88 Additional computational studies have been performed in an effort to assist in the experimental identification of this parent diboron(4) compound,89,90 as well as in the study of the interaction between B2H4 with proton donors, such as HF, HNC, HCl, HCN, and HCCH.91 The calculations showed that the diboron(4) compound interacts with the proton donors to form hydrogen-bond complexes with C2v symmetry. The elusive B2H4 species has been subsequently detected and analyzed using photoionization mass spectrometry and found to be consistent with the doubly bridged C2v structure for both neutral and ionic forms.12 Interestingly, early computational work using the MNDO method has shown that in the reaction of B2H4 with ethylene, a three-centered π-complex arising from electron donation of the alkene to only one boron atom is preferred over a four-centered intermediate.92 Furthermore, a recent publication by Cheng et al. reported the observation of a novel B2H4 prototype compound, with a molecular structure containing two terminal and two bridging hydrogen atoms, from irradiation of diborane(6) dispersed in solid neon at 3 K.93 The photochemically formed diboron(4) species showed many new absorptions in both the infrared spectrum and the ultraviolet absorption and emission spectra. One of the sets of absorptions, determined by analysis of the isotopic shifts of 10B and 11B, was identified as the diboron(4) species.93 While the parent compound has continued to elude synthetic chemists, the B2H4 molecule has been captured with the use of Lewis bases, such as phosphines and amines. Numerous examples exist in the literature in which adducts of B2H4 have been synthesized by cleavage of larger polyhedral borane complexes.94−100 For example, the bis-phosphine adduct (Ph3P)2·B2H4 was originally prepared by the addition of excess triphenylphosphine to (Me3N)·B3H7 in benzene at 50 °C.99 Kodama and co-workers elegantly used these adducts as building blocks for a variety of borane framework expansion reactions to generate higher order polyhedral boranes.101−107 The only other application of these base-stabilized species has been in their use as ligands for transitions metals, where the borane usually coordinates to one metal center using one or two M−H−B interactions.108−120 An interesting exception was the formation of a rare cobalt complex bridged by a nonsubstituted borylene (BH) group, which was isolated by treatment of Co2(CO)8 with a 2-fold excess of (Me3P)2·B2H4 (Scheme 3).108 A report by Himmel and co-workers confirms that bonding with group 6 metals occurs primarily through the hydrogen atoms; however, base-stabilized diboron(4) interactions with

2.3. B2(NR2)4 Compounds

A significant breakthrough in diboron(4) chemistry arose with the discovery of tetrakis(dimethylamino)diboron(4), B2(NMe2)4.123 In 1954, Urry and co-workers observed the formation of B 2 (NMe 2 ) 4 in the reaction of diboron tetrachloride with dimethylamine but only gave elemental analysis as evidence.64 It was not until 6 years later that a more convenient route to prepare this important compound was developed by Brotherton and co-workers.123 In this report, the diboron species was prepared by the addition of halobis(dimethylamino)boranes to highly dispersed molten sodium. Three equivalents of the starting monohaloboranes B(NMe2)2X were generated via a comproportionation reaction with 2 equiv of B(NMe2)3 and 1 equiv of the corresponding boron trihalide (BX3). Furthermore, Brotherton and coworkers also observed that transamination with a number of secondary amines gave the corresponding aminodiboron(4) species with loss of dimethylamine (Scheme 4).123 Two years later, Silver and co-workers reported that by using a similar transamination reaction with several different difunctional aliphatic secondary diamines and trimethylenediamine, a monomeric diboron compound with the general formula B2(NR(CH2)nNR)2 was formed upon the release of dimethylamine from tetrakis(dimethylamino)diboron(4).124 The structures of these diboron compounds, B2(NR(CH2)nNR)2, were analyzed further by Shore using mass spectrometry125 and the crystal structure was initially reported by Nöth and co-workers in 1976.126 In 1984, Nöth and co-workers reported adducts of these compounds from the reaction of B2(NR(CH2)nNR)2 with various trihalides, EX3 (E = B, Al, Ga; X = Cl, Br, I).127 The Lewis acid binds to the N atom on the backbone of the diboron compound, with both mono- and diadducts of the diamino compound observed, depending on the equivalents of EX3 used. Furthermore, it is noteworthy that B2(NMe2)4 also reacted with H2S to form heterocycles containing B2(NMe2)2 fragments bridged by two sulfur atoms.128,129 An interesting use for these compounds was investigated by Patton and coworkers, who discovered a novel synthetic pathway to various diboron-bridged bis(amide)−base complexes, starting from tetrakis(dimethylamino)diboron(4) (Scheme 5).130 This was initially reacted with HCl to form the mixed diamino−dichloro diboron compound, before reaction with the respective lithium D


Chemical Reviews

Review

Scheme 4. Formation and Reactivity of Tetrakis(dimethylamino)diboron(4), B2(NMe2)4

structural features and photophysical properties of these compounds.177

Scheme 5. Synthesis of Metal Complexes with Mixed Diaminodiboron Species

Scheme 6. Synthesis and Reduction of Dithieno-1,2-dihydro1,2-diborin

Power and co-workers178 and Nöth and co-workers168 prepared diboron(4) compounds containing mesityl groups, which show dramatically enhanced stability over their tert-butyl analogues. Actual applications of these compounds have so far been surprisingly limited; however, the landscape of synthetic chemistry changed drastically with the advent of dialkoxyborane(4) compounds. 2.5. B2(OR)4 Compounds

2.5.1. Synthesis of B 2 (OR) 4 . The parent B 2 (OR) 4 compound, B2(OH)4, is normally prepared through the hydrolysis of B2X4,179−181 B2(OR)4,154 or B2(NR2)4123,156 species. In the solid state, B2(OH)4 is found to exist in hydrogen-bonded sheets. The B−B bond lengths for two crystallographically inequivalent molecules are 1.715(5) and 1.710(4) Å.181 In a serendipitous reaction, trace amounts of water in the presence of B2(NMe2)4 allowed for the formation of a six-membered ring containing two B2(OH)2 fragments bridged by two oxygen atoms, a presumed intermediate in the formation of [BO]x polymers (Figure 4).182

anilinide to form the predicted diboron(4). The lithium salt was then reacted with several different transition metals to synthesize the desired complex.130 Unlike the subhalide derivatives, B2(NMe2)4 is stable in air up to 200 °C, although it is still moisture sensitive. This stability was believed to be due to extensive N−B π-bonding and steric crowding of the dimethylamino group (Scheme 4). The molecular structure of this species was determined using electron diffraction in 1981, and the amino groups were reported to adopt a fully staggered conformation (D2d), presumably for steric reasons. 131 While a number of tetraaminodiboron(4) compounds are now known,28,132−159 the angle of rotation about the B−B bonds in their solid-state structure usually lies in the range between 55° and 90°, depending upon the steric requirements of the amido groups.159

Figure 4. Formation of novel compounds containing B4O2 rings.

In their seminal work, Brotherton and co-workers also established a general route to dialkoxyborane(4) compounds by addition of alcohols to B2(NMe2)4 (Scheme 7, route 1).154 Several modifications to this synthetic procedure have occurred over the following decades26,28,29,155,183−187 including a selective reduction of specifically substituted halocatecholboranes. Additionally, Hartwig established a novel synthetic route to prepare a series of previously known substituted bis(catecholato)diboron(4) compounds in moderate to high yields by the reaction of 1% sodium/mercury amalgam with the corresponding halocatecholboranes (Scheme 7, route 2).188 A recent study by Braunschweig and Guethlein has shown that both B2pin2 and B2cat2 can be prepared by the metal-catalyzed dehydrogenative coupling of the starting boranes HBpin and HBcat, respectively (Scheme 7, route 3).189−191 These studies were based on previous observations by Marder et al., who observed the formation of B2pin2 from the rhodium-catalyzed dehydrocoupling of HBpin; however, there were only ca. 7 turnovers, with the major product being the C−H borylation of

2.4. B2(alkyl)n Compounds

In an attempt to enhance the applicability of these compounds, a number of second-generation diboron(4) compounds, based on tetrakis(dimethylamino)diboron(4), have been prepared and studied. Although a few mixed amino and halide compounds have been synthesized,128,160,161 a significant amount of research has focused on generating organoborane(4) derivatives containing B−C bonds.68,162−175 Of synthetic interest is a report by Wakamiya, Yamaguchi et al., who prepared and studied the boracycle dithieno-1,2-dihydro-1,2diborin and its dianion as potential building blocks for extended π−electron systems for making optoelectronic materials (Scheme 6).176 The same group went on to synthesize two other diarene-fused diborin dianions and investigate the E


Chemical Reviews

Review

Scheme 7. Synthetic Routes to Tetraalkoxydiboron(4) Compounds

Scheme 8. Reactions of Platinum−Phosphine Complexes with Catecholborane

the benzene solvent.192 This methodology is extremely important as it allows for a new one-step procedure, from easily prepared boranes to two of the most widely used and synthetically pertinent diboron(4) compounds. Marder, Braunschweig and co-workers also reported the reverse reaction, namely, the synthesis of boranes from diboron(4) compounds via hydrogenolysis of the B−B bond, using heterogeneous Group 10 catalysts, with palladium on charcoal found to be the most effective.193 Hartwig et al. observed a similar reaction taking place to generate DBpin via the deuterolysis of B2pin2, catalyzed by an iridium complex.194 A recent experimental and computational study has gathered evidence for several postulated intermediates in the platinumcatalyzed dehydrocoupling of HBcat, including a platinum boryl hydride species, resulting from the oxidative addition of HBcat, and a platinum bis-boryl species.191 Bulky cyclohexyl groups from the phosphine ligands block reaction of the metal center with a second equivalent of HBcat, preventing dehydrocoupling and allowing for the isolation of the trans-hydridoboryl platinum species (Scheme 8, left). More flexible P(CH2Cy)3 ligands allow for reaction with a second equivalent of borane, prompting dehydrocoupling and the formation of B2cat2 (Scheme 8, right). A similar process was also reported by Marder et al. in their investigations into the mechanism of the rhodium phosphine-catalyzed borylation reaction.192,195 The observed B2pin2 was computed to be generated via a reaction of a [(PiPr3)2Rh(Bpin)] species with HBpin.195 The development of new tetraalkoxydiboron(4) and related derivatives is an area that had received little attention, but of notable exception are the bis(dithiocatecholato)-, bis(catecholato)-, and bis(pinacolate)diboron(4) analogues29,33,187,196−200 and bis(neopentylglycolato)diboron (B2neop2, Figure 1),29 the latter two are now being widely used in catalytic borylation reactions. Interestingly, unsymmetrical diboron compounds are beginning to find a niche in organic synthesis as different reactivities and regioselectivities can be achieved in reactions using these unusual species. Therefore, compounds such as pinacolato diisopropanolaminato diboron (PDIPA, Figure 5),201,202 BpinBMes2,203 BpinBdan (dan = naphthalene-1,8-diaminato, Figure 5),204 and BpinBdab

(dab = 1,2-diaminobenzene) and derivatives205,206 are becoming more significant (vide infra).

Figure 5. Alternative dialkoxydiboron(4) compounds.

A recent study by Bryce and Perras showed an interesting development in the use of NMR spectroscopy to analyze B2(OH)4, several dialkoxyborane(4) species, and the literature known adducts of these compounds (vide infra).207 By using 11 B DQF J-resolved NMR spectroscopy, the J(11B,11B) values were shown to correlate with the energy of the B−B σ-bonding natural bond orbital (NBO). Therefore, this allows direct information to be obtained about the strength of the B−B bond and the hybridization of the boron orbitals involved in this bond.207 2.5.2. Adducts of B2(OR)4 Compounds. Lewis acid−base adduct formation of B2cat2 was examined with 4-picoline, and the addition of 1 equiv of base led to rapid exchange between the two boron atoms (Scheme 9, route 1).208 Addition of a second equivalent of 4-picoline proceeded to give the bis(adduct) (Scheme 9, route 2).208 Further studies by Ingleson and co-workers showed that, under specific solvent conditions, the 1,2-B2cat2·(pic)2 isomer could be isolated and crystallized.209 Additionally, alternative Lewis base adducts of B2cat2 were structurally characterized, confirming the formation of F


Chemical Reviews

Review

Scheme 9. Lewis Base Adducts of B2cat2 with 4-Picoline

the exchange involved dissociation and reassociation of the NHC rather than an intramolecular pathway. 213 The monoadduct was isolated and structurally characterized by Xray diffraction.213 Further investigations of the NHC adducts of diboron(4) compounds, such as B2cat2, were investigated in a collaboration among the Marder, Radius, and Ingleson groups.216 Initially, the adduct B2cat2·Me4Im was isolated (Figure 6), but unlike the previous NHC adduct of B2pin2, no dissociation of the NHC was observed on the NMR time scale. The bis-adduct B2cat2·(Me4Im)2 was also synthesized and structurally characterized by solid-state NMR spectroscopy. More interestingly, it was observed that, unlike the monoadduct, the bis-adduct was unstable at elevated temperatures and underwent ring expansion of the NHC to form a sixmembered hetereocycle after several hours (Figure 6).216,217 The interest in Lewis base adducts of B2pin2 has grown over the past few years, due to the proposed requirement of such compounds in the catalytic cycle of borylation reactions, in the presence or absence of a transition metal (vide infra).43,45,218−222 The formation of such compounds had been proposed by Miyaura and co-workers as early as 2000223 as a means of enhancing the nucleophilicity to generate a boryl anion equivalent. Miyaura et al. thus proposed that the in-situ formation of [B2pin2OAc]− aided in the formation of a Cu− boryl complex, required to facilitate the copper-catalyzed βborylation of α,β-enones.223,224 Furthermore, anionic adducts, such as [B2pin2OR]−, have been discussed and observed in computational and spectroscopic studies;219,221,222,225−231 however, the full characterization of a series of anionic sp2− sp3 Lewis base adducts of B2pin2, such as [K(18-Crown6)][B2pin2OMe] and [Me4N][B2pin2F], was only published recently by Marder et al. (Figure 7).218,232 The reactivity of these isolated adducts with aryl electrophiles will be discussed later (section 5.5). In comparison, Santos et al. reported a similar neutral intramolecular sp2−sp3 diboron(4) compound, in the absence of base.201,202 The interaction of the amino group with one of the boron centers alters the hybridization of the B moiety from sp2 to sp3, providing a more nucleophilic Bpin fragment, which accelerates the transmetalation step in

both 1,1 and 1,2 isomers of B2cat2 with DBN (1,5diazabicyclo[4.3.0]non-5-ene).209 Phosphine adducts of bisthiocatecholato196 are known, though only (mono and bis) PMe3 adducts have been suggested with B2cat2.210 Other bisdithiolatodiboron species and their adducts have been prepared by Norman and co-workers.161,211 Despite the lack of evidence for adduct formation at room temperature by solution NMR spectroscopy, cocrystals of 1:1 complexes between TCNQ (7,7,8,8-tetracyano-p-quinodimethane) or TCNE (tetracyanoethene) and B2cat2 or bis(dithiocatecholato)diboron have been isolated and structurally characterized.212 A detailed NMR spectroscopic study with B2pin2 and the NHC, 1,3-bis(cyclohexyl)imidazol-2-ylidene, revealed that rapid exchange of the NHC between the two boron atoms was occurring in solution (Figure 6).213 The adduct was initially proposed by Hoveyda to be involved in metal-free borylation of α,β-unsaturated compounds214 and its NMR assignment corrected subsequently.215 DFT calculations suggested that

Figure 6. NHC adducts of diboron(4) and the ring-expansion product formed from B2cat2·(Me4Im)2 (RER = ring-expansion reaction). G


Chemical Reviews

Review

Figure 7. Anionic sp2−sp3 adducts of B2pin2.

2.7. Diboryl Groups as Ligands

the copper-catalyzed borylation of electron-poor olefins (section 4.1).202 Several anionic adducts of [B2pin2R]− have also been observed in NMR studies but without crystallographic evidence.233,234 In 2014, Wang and co-workers discovered that the boryl−borate, Li[B2pin2Ph]·1/8B2pin2, formed a frustrated Lewis pair with B(C6F5)3 that could activate dihydrogen, pinacolborane, and ethylene (Figure 7),234 while Bedford et al. observed the formation of the adduct Li[B2pin2tBu] by 11B NMR spectroscopy from the reaction of B2pin2 with tBuLi.233 Anionic adducts of unsymmetrical diboron(4) compounds have also been synthesized. Kleeberg and co-workers showed that an unsymmetrical diboron(4) compound, BpinBdmab (dmab =1,2-di(methylamino)benzene), reacted with [K(18Crown-6)OtBu] to form an anionic sp2−sp3 adduct, [K(18Crown-6)][BpinBdmabOtBu], with the tert-butoxide group attached to the more Lewis acidic Bpin moiety.205 Yamashita et al. also observed the formation of a diboran(4)yl radical anion, [K([2,2,2]-cryptand)]+[BpinBmes]•−, from the reduction of BpinBMes2.235

In the late 1990s, Braunschweig and co-workers began reporting reactions of diamino−dichloro diboron(4) compounds with transition metals. An early reaction with 2 equiv of an anionic manganese hydride complex resulted in the formation of a borylene-bridged bimetallic species (Scheme 11, see also Scheme 3 for a similar reaction).241−247 Reactions Scheme 11. Synthesis of Borylene-Bridged Bimetallic Species from Anionic Manganese Hydride Complex

of related diboron(4) compounds with sodium salts of anionic iron and tungsten complexes resulted in an anion exchange and the formation of transition-metal-substituted diboron(4) compounds.49,245,246,248−250 Analogous reactions were carried out with potassium salts of anionic molybdenum and ruthenium complexes.251,252 Platinum(II) diboryl complexes could be formed from the oxidative addition of B−X bonds of B2X2(NMe2)2 at zerovalent platinum centers.253 These diboryl groups were found to have a strong trans influence, resulting in a lengthening and labilizing effect on trans-Pt−Br and Pt−I bonds compared to the dihaloboryl analogues.253 In a unique reaction, the addition of a chelating diphosphine ligand to trans-[Pt(PiPr3)2Br(B(NMe2)B(NMe2)Br)] not only displaced phosphine ligands from the platinum complex but also resulted in rearrangement to a cisbis-boryl species (Scheme 12, left).254 This reaction is presumed to proceed through rearrangement and reductive elimination of the dibromodiboron, followed by a subsequent oxidative addition of the boron−boron bond. Reaction of other zerovalent platinum tetraphosphine compounds with B2X2Ar2 also resulted in oxidative addition of the boron−halogen bond.255,256 The products of these reactions show a significant interaction between the electron-rich metal center and the βboron atom, due to its electron deficiency. The magnitude of this interaction was found to be strongly dependent on the halide substituent. A platinum(II) diboryl complex could also be reduced to a platinum zero diborene complex by a magnesium(I) dimer (Scheme 12, right).257,258 It is noteworthy that the diboron B2I2(NMe2)2 undergoes oxidative addition when reacted with 2 equiv of Pt(PEt3)3, forming a bimetallic species bridged by a diboron(4)-1,2-diyl ligand.259

2.6. Three-Membered Aromatic Heterocycles Containing B−B Bonds

A unique class of compounds possessing a boron−boron bond contains a three-membered aromatic ring, where two πelectrons are shared between the three atoms. Thus, the boron−boron bonds tend to be somewhat shorter than single bonds, owing to the aromatic character of these species. Of those systems containing boron−boron bonds, B32−, B2C−, and a variety of B2E (E = NR, O) heterocycles are known.133,236−240 In the case of azadiboriridines (E = NR), steric bulk is vital to prevent dimerization (Scheme 10, left). Although some of these Scheme 10. Reactions of Azadiboriridines

2.8. [2]-Borametalloarenophanes

[2]-Boraferrocenophanes are a unique family of organometallic complexes containing a boron−boron bridge between the two cyclopentadienyl rings of ferrocene. The parent compound (Scheme 13, center), was first prepared by Herberhold, Dörfler, and Wrackmeyer through the reaction of dilithioferrocene with B2Cl2(NMe2)2.260 A closely related species containing sulfur atoms between each boron atom and the cyclopentadienyl rings

heterocycles have proven to be quite reactive in B−B addition chemistry (Scheme 10), generation of these species involves lengthy and highly air- and moisture-sensitive procedures, limiting their synthetic utility. H


Chemical Reviews

Review

Scheme 12. Synthesis and Reactions of Platinum(II) Diboryl Complexesa

a

dur = 2,3,5,6-Me4C6H.

active catalysts in ethylene polymerization and ethylene/1hexene copolymerization.262,275

Scheme 13. Reactions of [2]-Boraferrocenophanes with B2(diol)2 and Pt(PEt3)3

2.9. B−B Bonding

Much like its neighbor in the periodic table, carbon, boron can form a wide variety of homoatomic bonds. In addition to single, double, and triple bonds, singly reduced diboron(4) compounds having a formal bond order of 1.5 are also known.162,173,247,258,276−285 The discussion here will be confined to diboron(4) species and reactions of these species. Most diboron(4) compounds have a relatively simple structure with a single B−B bond and no bridging atoms; however, there are some examples of species with bridging hydrides. The simplest diboron(4) compound, B2H4, was found to have a doubly bridged C2v structure (section 2.2) by photoionization mass spectrometry.12 The staggered D2d isomer was found to have a very similar energy. Though rare, the doubly bridged B2(μ-H)2 core has been observed under ambient conditions using very bulky aromatic terminal substituents (Scheme 14a).170 The B−B bond length of 1.4879(7) Å observed in the molecular structure of the hydrogen-bridged species was found to be significantly shorter than experimental values for neutral B−B double bonds (1.560(18)281 and 1.546(6) Å282) but comparable to experimental (1.449(3) Å)282 and calculated (1.455 Å)286 values for B−B triple bonds. The short distance along with nearly linear B−B−C bond angles implied sp hybridization, an assertion that was confirmed through a computational study.170 Thus, the species can be considered to contain a doubly protonated basic boron−boron triple bond.

was prepared by Norman and co-workers.261 Braunschweig and co-workers subsequently developed a synthesis for the biscyclopentadienyl-diboron ligand, allowing for the preparation of other transition-metal complexes.262 Related sandwich complexes containing B−B bonds as bridging atoms were prepared either through anionic diboryl species263−266 or via deprotonation of the transition-metal precursor and subsequent addition of dichlorodiborons.267,268 For example, the reaction of 2 equiv of lithioferrocene with B2Cl2(NMe2)2 generated the diboronbridged bis-ferrocene complex Fc(NMe 2 )BB(NMe 2 )Fc.68,264,269 The B−B bond in [2]-borametalloarenophanes has been cleaved by addition to alkynes using palladium and platinum catalysts, inserting the carbon−carbon triple bond into the B−B bridge.270−273 Braunschweig and co-workers were also able to isolate heterobimetallic compounds resulting from oxidative addition of the B−B bond to a platinum(0) compound (Scheme 13, right).267,268,271,274 Reaction with B2pin2 or B2cat2 resulted in boryl exchange and loss of the B−B bridge (Scheme 13, left).270 Additionally, these complexes were found to be

Scheme 14. (a) Synthesis of the Stable Doubly Hydrogen-Bridged Diboron B2Eind2(μ-H)2, and (b) Synthetic Route to the Isolable Diboron(4) Compound B2(MPind)2H2 and the Diboron B2Eind2(μ-H)2

I


Chemical Reviews

Review

Scheme 15. Reactions of B2Br2Mes2 with PEt3 and PMeCy2

Further studies by Tamao et al. observed the first isolable diboron(4) compound with terminal B−H bonds in both solution and the solid state (Scheme 14b).287 The terminal B− H bonds were protected by 1,1,7,7-tetramethyl-3,3,5,5tetrapropyl-s-hydrindacen4-yl (MPind) groups, which are bulkier than the Eind group previously used, and therefore aid in stabilizing the compound with terminal hydrogens. The characteristics of the compounds were shown to be very different, with the MPind-based diboron compound having a single B−B bond, compared to the multiple bonding character shown previously in the Eind-based compound.287 Bridging halides have also been observed by Braunschweig and co-workers upon adding a phosphine to Mes(Br)BB(Br)Mes (Mes = 2,4,6-trimethylphenyl).288 The bridging bromide was found to have a minimal impact on the B−B bond length; however, the bond angles at boron differed significantly from the idealized sp2 and sp3 geometries. The product distribution in the reaction was found to depend heavily on the steric bulk of the phosphine (Scheme 15). An analogous rearrangement of B2X2Mes2 involving 1,2-migration of the mesityl group has been previously observed in the reaction of B2Cl2Mes2 with an N-heterocyclic carbene.289 Remarkably, Braunschweig and co-workers reported the synthesis of 5 different product types based on the reaction of a Lewis base with B2X2R2 species through variation of the base used and the groups present on the diboron compound (Scheme 16).290 Increasing bulk of the base and halide was found to increase the likelihood of halide migration. Yet another type of product was observed when 2 equiv of NEt3 was added to B2I2Mes2 in pentane. Precipitation of Et3N−HI was observed along with the product of an intramolecular C−H activation of the NHC-NtBu group; the remaining iodine atom

adopts a bridging position (Scheme 16, right).291 A recent report by the same group expanded upon the scope of Lewis base addition to unsymmetrical diboron(4) compounds, demonstrating the formation of adducts of 1,1-dimesityl-2,2difluorodiboron with Lewis bases attached, somewhat surprisingly, to the more sterically congested diaryl boron atom.292 Though covalently bound bidentate substituents generally bind to one boron atom, there are several cases in which these substituents are covalently bound to each boron atom. In 1994, Siebert and co-workers produced one such compound through reaction of Li2(1,2-(CH2)2C6H4) with B2Cl2(NMe2)2.293 This compound was found to insert an alkyne, resulting in ring expansion. A related species was produced by Lesley, Norman, and co-workers through the reaction of disodium catecholate with B2Cl2(NMe2)2 (Scheme 17a, right).294 They noted that the B−B bond in this cyclic species is slightly longer than that of B2cat2. Surprisingly, the authors found that the analogous reaction of B2Cl2(NMe2)2 with dilithium thiocatecholate produced the 1,1-isomer (Scheme 17a, left). A molecular mechanics study has suggested that 1,1-diboron compounds are generally more stable than their cyclic 1,2-counterparts.295 Norman and co-workers prepared a variety of 1,1- and 1,2diaminodiboron species and found that the binding mode depended on the diamine used.132 In the case of 1,2diaminobenzene, a mixture of 1,1- and 1,2-isomers was prepared by reaction of the diamine with B2(NMe2)4 (Scheme 17b).160 The molecules were easily separated due to the poor solubility of the 1,2-derivative. Molecular structures reveal that the B−B bond length is significantly contracted in the 1,2derivative (1.649(3) and 1.651(3) Å vs 1.678(5) Å for the 1,1isomer). Likewise, the B−N bond lengths also contract. Lithiation of the 1,1-derivative, followed by reaction with 2 equiv of Cl(NMe2)BB(NMe2)Cl, formed a new polycyclic borazine species.296 A tetra-N-methylated derivative of the bis1,2-phenylenediaminato derivative could be quantitatively oxidized to a radical cation using Ag[Al(OC(CF3)3)4].297 An X-ray crystallographic study revealed that this oxidation caused a contraction of C−N bond lengths in one ring but had no effect on the B−B bond length. One-electron reductions have been known for diborons for quite some time, and the products were initially characterized by EPR spectroscopy.298 Structural characterization of these singly reduced monoanionic species show B−B distances shortened by approximately 5%, with a formal π-bond order of 0.5.280 Similarly, these species with one-electron π-bonds are accessible through the oxidation of electron-rich diborene compounds.299 Two-electron reductions of diboron(4) compounds increase the formal π-bond order to 1; however, the boron−boron contacts do not shorten substantially, an effect explained by the repulsive effect of adjacent negative charges on each boron atom in the dianion.162,173,278−280 In a related reaction reported by Wagner and co-workers, the one-electron reduction of a biaryl bis-borane gave a one-electron σ-bond, the first time this type of bonding has been crystallographically

Scheme 16. Reactions of B2R2X2 with Lewis Bases

J


Chemical Reviews

Review

Scheme 17. (a) Reactions of B2Cl2(NMe2)2 with Dilithium Thiocatatecholate (left) and Disodium Catecholate (right); (b) Reaction of 1,2-Diaminobenzene with B2(NMe2)4

characterized (Scheme 18).300 A boron−boron bond length of 2.265(4) Å was observed.

sluggish, presumably as a result of the reduced Lewis acidity at boron arising from increased π-dative bonding with the smaller fluorine atoms. These uncatalyzed diboration reactions generally yield cis-1,2-addition products. This type of reaction was initially thought to proceed via a 4-centered transition state with the unsaturated substrate coordinated to the vacant p-type orbitals on both boron atoms; however, subsequent computational studies of reactions of B2H4 with ethylene92 and acetylene302 using the MNDO method revealed that this substrate−diboron interaction was taking place through just one of the boron atoms. This initial interaction results in a significant lengthening of the B−B bond, and the rearrangement of this adduct intermediate to the diboration product is nearly thermoneutral. While these early diboration reactions were generally successful, compounds with B−Cl bonds are quite air and moisture sensitive; therefore, recent developments have focused on diborations with more stable, electron-rich heteroatomsubstituted diboron sources.70 However, these more electronrich diborons are generally not as reactive, due to the reduced Lewis acidity at the boron center; thus, transition-metal catalysts are often required. Their ease of synthesis, stability, and moderate reactivity have made B2(OR)4 species preferred diboron reagents. In particular, bis(pinacolato)diboron (B2pin2), bis(catecholato)diboron (B2cat2), and BpinBdan have recently been extensively used in transition-metalcatalyzed reactions.

Scheme 18. Formation of a B·B One-Electron σ-Bond Confirmed by X-ray Crystallography

Power and co-workers found that some dianions can undergo intramolecular C−H or C−C bond activation (Scheme 19).173 They proposed that these rearrangements proceed through initial reduction, followed by loss of a methoxide group. A similar C−H bond activation of a mesityl group was observed by Braunschweig and co-workers upon reduction of an NHC adduct of Cl2BBMes2 (Scheme 16).289 A comprehensive summary of reductions of B−B bonds was published by Braunschweig and Dewhurst.247 The boron−boron single bond found in typical diboron compounds is approximately 1.7 Å (2 × 0.85 Å, the approximate atomic radius for boron) and is quite electron rich due to the relatively electropositive nature of boron.

3. 1,2- AND 1,4-DIBORATIONS This section will focus on reactions of diboron(4) compounds where both boryl (BR2) groups are added to the substrate. Uncatalyzed reactions of this type using diboron tetrahalides have been known for quite some time but were often uncontrollable and gave unstable products (see section 2.1).301 The addition of B2Cl4 to a variety of unsaturated substrates proceeds in the absence of catalyst, often at low temperatures. Analogous reactions of B2F4 are much more

3.1. Mechanistic Studies of 1,2-Diboration Processes

Platinum(0) complexes have generally proven to be the most effective and general catalysts for diboration reactions.53,68,70,301 While the substrate scope for this reaction is quite extensive31,32,52,53 and includes alkynes, alkenes, dienes, allenes, vinyl boronate esters, carbonyls, unsaturated carbonyls, and imines, the mechanisms are often quite similar. Mechanistic studies suggested that the catalytic cycle proceeded via initial

Scheme 19. Intramolecular C−H (left) and C−C (right) Bond Activations by 2,6-Dimesitylphenyl-Substituted Diborons

K


Chemical Reviews

Review

oxidative addition/reductive elimination of B2(OMe)4 at platinum(0) is reversible and temperature dependent.318 A similar phenomenon was reported by Smith and co-workers in their investigations into the catalytic capability of [Pt(PR3)2(B(OR)2)2] in the diboration of alkynes (vide supra).312 It was observed that [Pt(PPh3)2(Bcat)2] could be generated along with B2pin2 from the reaction of [Pt(PPh3)2(Bpin)2] with B2cat2.312 Marder, Baker, and co-workers demonstrated alkene insertions into rhodium−boron bonds319 and oxidative addition of diborons at rhodium29,320 and iridium320,321 centers, suggesting that diborations using these metals as catalysts could proceed through a similar mechanism. However, σ-bond metathesis reactions between rhodium(III) bis-boryl species and other diboron compounds suggest the mechanism may be somewhat more complex.322 Oxidative addition of B2cat2 with a rhodium(I) boryl complex has also been observed, resulting in the generation of a rhodium(III) tris-boryl complex.323 Perutz, Marder, and co-workers later showed oxidative addition of B2pin2 to a rhodium(I) center.324 Cobalt(0),325,326 osmium(0),327,328 and ruthenium(0)328 complexes were also found to oxidatively add B2cat2 (Scheme 21). Similar oxidative

oxidative addition of the diboron(4) species to the metal center, followed by coordination of the unsaturated substrate and insertion into one of the Pt−B bonds. A subsequent reductive elimination afforded the corresponding product and regenerated the active catalyst (Scheme 20).245,303 Early Scheme 20. Proposed Catalytic Cycle for the Diboration of Alkynes Using Zerovalent Platinum Complexes

Scheme 21. Oxidative Addition Reactions of B2cat2 at Zerovalent Cobalt, Osmium, and Ruthenium Centers

computational studies have shown that the initial oxidative addition step is unlikely to occur in the case of palladium complexes.56,112,304−306 However, a more recent study has contradicted these early works, demonstrating that B−B oxidative addition can occur at zerovalent palladium centers.307 Experimental evidence has been found for each step of the catalytic cycle.49,56 Marder and Norman reported the crystal structures of the organic products from the diboration of alkynes with either B2pin2308 or B2cat2.309 The groups of Marder 310 and Smith311,312 reported the isolation and characterization of [Pt(PR3)2(B(OR)2)2] complexes, which proved to be catalytically competent in the diboration of alkynes. These species were, in fact, found to be more active than the initially used catalyst precursor Pt(PPh3)4.313,314 In the same studies, further evidence was gathered that suggested that phosphine dissociation is a key step in the reaction. If a c h e l a t i n g bi s - p h o s p h i n e s u c h a s d p p e ( 1 , 2 - b i s (diphenylphosphino)ethane) is used instead of two monodentate phosphine ligands, the platinum complex is found to be catalytically inactive. The addition of excess phosphine to the reaction mixture was also found to slow the reaction significantly. Other studies have shown base-free metal complexes to be effective catalysts for 1,2-diboration reactions.315,316 Later, Norman and co-workers reported the oxidative addition of a variety of diborons, including B2(X4cat)2 (X = Cl, Br)200 and Cl(NMe2)BB(NMe2)Cl210 to zerovalent platinum centers. Braunschweig and co-workers examined the reductive elimination of (alkyl)Bcat from platinum(II) complexes upon addition of excess B2pin2 or B2cat2 or alkynes; however, they were unable to distinguish between metathesis and reductive elimination pathways.317 The same group also recently discovered a system where the

addition reactions of substituted bis(catecholato)diborons(4) have been observed with Fe(CO)4329 and Cp2W,330 generated in situ from Fe(CO)5 and Cp2WH2 (or [Cp2WH(Bcat)]), respectively, using photolysis. Products of B2F4 oxidative addition to platinum and iridium centers are also known.331,332 A report in 2007 described oxidative addition using a variety of diborons with Pt(PMe3)4, resulting in the loss of two phosphine ligands and the formation of square planar platinum(II) complexes.333 Reaction of Vaska’s compound, trans-[Ir(CO)Cl(PPh3)2], with B2F4 generated fac[Ir(BF2)3(PPh3)2(CO)] (Scheme 22).334 Presumably, the Scheme 22. Reaction of Vaska’s Compound with B2F4

chloride ligand from Vaska’s compound is lost through transmetalation or reductive elimination as BF2Cl. Attempts to isolate products from the reaction with just 1 equiv of B2F4 were unsuccessful. Thus, the oxidative addition/reductive elimination mechanism depicted in Scheme 20 has also been implicated in diboration reactions catalyzed by other metals, including some rhodium(I)335−341 and palladium cataL


Chemical Reviews

Review

Scheme 23. Generation of a Nickel(II) Boryl Complex via Addition of B2cat2 to a Nickel(II) Alkoxide Species (left) and a Nickel(I) Dimer (right) by Mindiola and Co-workers

lysts.307,342 While rhodium(I) catalyst systems are usually believed to proceed through an oxidative addition/reductive elimination mechanism (Scheme 20), mixtures of products are often observed as β-hydride elimination can compete with reductive elimination, generating borylation or dehydrogenative borylation products. Marder and co-workers found that B2cat2 is, not surprisingly, more active in transition-metal-catalyzed alkyne diborations than B2pin2, while the B2(4-tBucat)2 is less active than B2cat2.310 It is significant to note at this time that organoboron products containing Bpin groups are relatively stable to air, moisture, and column chromatography and thus offer a synthetic advantage over their catecholato counterparts, which decompose in air. While many 1,2-diborations operate through the oxidative addition/reductive elimination mechanism outlined above, other reports have highlighted similar additions, which are not believed to operate via this mechanism. In particular, the ability of copper(I) complexes to catalyze the diboration of unsaturated organic molecules is emerging as a remarkably useful synthetic tool.70,343−345 This reaction operates through a series of σ-bond metathesis steps, resulting in the overall transfer of two boryl groups to the substrate. Other catalysts believed to proceed through a similar mechanism include gold nanoparticles,346 palladium(II)−NHC complexes,48,347 and some iridium catalysts.204,348 Mindiola demonstrated stoichiometric σ-bond metathesis reactions of nickel(II) and cobalt(II) tert-butoxide complexes with B2cat2 and B2pin2, respectively, to generate metal−boryl species (Scheme 23, left).349 The nickel(II) boryl species is also accessible through addition of B2cat2 to a nickel(I) dimer (Scheme 23, right).350 In the case of copper(I) catalysts, the reaction has been studied extensively through density functional theory (DFT) calculations.43,351−353 Further support for the stepwise transfer of boryl groups (Scheme 24) was shown by Fernández and coworkers, who were able to generate the mixed bis-borylalkane

through the use of two different diborons, suggesting that each boryl group of the product came from a different diboron molecule.346 An intriguing recent discovery by Fernández and co-workers is that diborations of various unsaturated substrates with B2pin2 can take place without a transition-metal catalyst.225−227,354 An excess amount of alcohol and a catalytic amount of a base are present and serve to generate the catalytically active anionic species, [B2pin2OR]−, which is an alkoxide adduct of B2pin2 (for further information see section 2.5.2). Upon formation of this adduct, the boron−boron bond becomes strongly polarized and interacts with the substrate.219 It was proposed that the intermediate rearranges to the diboration product, while the alkoxide ion is abstracted from the product by protonation (Scheme 25). The use of a chiral alcohol produced diboration Scheme 25. Proposed Catalytic Cycle for the Metal-Free Diboration of Alkenes

products with modest enantiomeric excesses (ee’s).226 These promising reports highlight an efficient, affordable, and quite environmentally benign method to generate 1,2-diboron species and their corresponding 1,2-diols.351,355,356 One example has emerged in the literature showing B−B addition across nitrogen−palladium bonds (Scheme 26),357 suggesting another plausible mechanism to consider for this

Scheme 24. Proposed Catalytic Cycle for the Diboration of Alkenes Using Copper(I) Complexes

Scheme 26. Addition of B2cat2 across a Palladium−Nitrogen Bond

M


Chemical Reviews

Review

Scheme 27. Functionalization of Alkyne Diboration Products

Scheme 28. Internal-Selective Cross-Coupling Reactions of 1,2-Diborylalkenes

Scheme 29. Catalyzed Diborations of Alkynes with [B(NMe2)Cl]2

supported platinum nanoparticles,363−365 and Co(PMe3)4.326 Nanoporous gold and platinum metals have also been found to be effective catalysts for the diboration of internal alkynes with B2pin2.366 While the platinum metal was found to leach into the reaction mixture, gold did not; thus, the heterogeneous gold catalyst was easily reused after washing with acetone. A crossaddition experiment using the nanoporous gold catalyst with B2pin2 and B2hex2 (hex = hexylene glycolato, 2-methyl-2,4pentanediolato) showed a mixture of products, including the cross-addition products, suggesting the reaction does not proceed through oxidative addition.366 The alkene products resulting from alkyne diboration contain two boron groups and can be further transformed to other useful organic molecules. For example, Morken and co-workers studied the rhodium-catalyzed asymmetric hydrogenation of these substrates as an effective method of ultimately generating 1,2-diols (Scheme 27, right).367 Electrophilic fluorination of these diboron products affords α,α-difluorinated carbonyl compounds (Scheme 27, left),368 which can be transformed subsequently into the corresponding imine derivatives.369 Armstrong and co-workers used a diborated internal alkyne for two subsequent Suzuki reactions, the second of which attaches the molecule to a solid support.370 Suzuki−Miyaura cross-coupling of alkyne diboration products with alkyl and aryl halides has been used in the synthesis of semiconductor materials, 371 tetrasubstituted alkenes, 372−374 benzo[b]oxepine,375 and 1-boryl-alkenes376 and the introduction of a methyl group to a cycloalkynone.377 While the majority of these diboration reactions utilize bis(pinacolato)diboron (B2pin2) or bis(catecholato)diboron (B2cat2), the use of BpinBdan as the diborating agent in Ir(I)and Pt(0)-catalyzed diborations provides access to unsymmetrically substituted bis-boronated alkenes, allowing for regioselectivity in subsequent cross-coupling reactions complementary to their symmetrical counterparts (Scheme 28).204,378 High regioselectivities were achieved for products bearing the naphthalene-1,8-diaminatoboryl group on the terminal carbon. The more inert electron-rich Bdan group protects the normally more reactive terminal position;376 thus, subsequent crosscoupling reactions occur selectively at the internal site. Lesley, Norman and co-workers demonstrated platinumcatalyzed alkyne diboration with Cl(NMe2)BB(NMe2)Cl

important reaction. Though the reaction results in cleavage of the B−B bond, it does not result in a net oxidation of the metal center. There are extensive examples of additions across metal− ligand bonds in the literature, most notably the addition of H2 across a metal−ligand bond in Noyori-type hydrogenation catalysis. This reaction suggests the possibility of delivering both boryl groups from the same diboron molecule to the substrate, without formal oxidative addition. 3.2. Alkynes

In general, terminal alkynes (RCCH) are considerably more reactive than the corresponding internal alkynes (RCCR′). Thus, an efficient yet regioselective method for adding boron reagents to internal alkynes remains a challenging problem. For example, hydroboration reactions are plagued not only by a mixture of isomers but also from products arising from a second addition reaction to the activated boron-containing alkenes. Remarkably, the first diboration reaction of alkynes was reported in 1959,83 where acetylene was observed to react with diboron tetrachloride at −45 °C. While garnering some initial attention,358 over 20 years would pass before a computational study was carried out on the diboration of acetylene with B2H4 using the MNDO method.302 The reaction was shown to be exothermic and proceed through an intermediate with the triple bond interacting once again with one boron atom. The reaction of B2Cl4 with other alkynes was subsequently studied and found to give the cis-1,2-diboration products.359 Interestingly, reactions of tBuClBBCltBu with TMS-substituted alkynes were found to yield 1,1-diboration products,360 thought to occur through rearrangement of the initially generated 1,2diboration product. The first synthetically relevant diboration of both internal and terminal alkynes was reported in 1993 by Miyaura, Suzuki, and co-workers using B2pin2 and a catalytic amount of a platinum(0) complex, typically Pt(PPh3)4.313 Alkenylboron products were generated in high yields (>90%) when reactions were carried out in DMF at 80 °C for 24 h in the presence of 3 mol % of a zerovalent platinum complex. The formation of the cis isomer was established with high selectivity (>99%). Subsequent studies resulted in the discovery of other effective catalyst precursors, including cis-[Pt(B(OR)2)2(PPh3)2] compounds,310,312 [Pt(PPh3)2(η2-C2H4)2],310 [Pt(COD)Cl2],315 Pt−isocyanide complexes,361 [Pt(PR3)(η2-C2H4)2],362 solidN


Chemical Reviews

Review

(Scheme 29).379 In this instance, the ability of the dimethylamine group to bridge the two boron atoms, along with the differing electronic effects of the chloride and dimethylamine groups, induced rearrangement of the diboron substituents in the product. B 2 pin 2 was found to add to alkynylboronates and alkynylphosphonates producing tris-boronated alkenes and cis-1,2-diboronated vinylphosphonates, respectively, provided that catalyst and diboron were heated together prior to addition of the alkyne.380 A noteworthy observation from this study is that hydrodeboronation of the alkynylboronate, presumably caused by the presence of trace amounts of water, was observed when substrate, catalyst, and diboron were mixed together simultaneously. The initial addition of diboron and the platinum catalyst likely removes trace water from solution, believed to occur through reaction of a platinum bis-boryl species with water, forming a platinum bis-hydride and an oxobridged diboron. Arynes, generated in situ, can also be diborated by B2pin2 with the Pt(dba)2/isocyanide catalyst system.361 Alternative substituents on the alkyne were recently examined by Nishihara and co-workers in the selective synthesis of vic-diborylated vinylsilanes from the relevant alkynylsilane and B2pin2374 and by Ohmiya and Sawamura in the diboration of alkynoates using a phosphine organocatalyst.381 The same authors went on to discover that similar reactions could be conducted with catalytic amounts of Brønsted bases, with the expansion of the substrate scope to incorporate propiolamides and 2-ethynylazoles.382 Furthermore, Uchiyama et al. utilized the presence of a hydroxy substituent in the trans-diboration of propargylic alcohols in the absence of a transition-metal catalyst (Scheme 30).383

Figure 8. F050 and F1070, two biologically active molecules prepared through the diboration (and subsequent Suzuki−Miyaura crosscoupling) of a transient aryne.

The authors believed this replacement to be caused by elimination of copper(I) methoxide from the organocopper intermediate, resulting in the formation of an allene, which is then inserted into a boron−copper intermediate. The insertion/CuOMe-elimination process is repeated with the intermediate allene, resulting in the formation of a 1,3-diene, which subsequently undergoes copper(I)-catalyzed 1,4-diboration.356,386,387 The selective diboration of bis(2-bromophenyl)acetylene with B2neop2 (neop = neopentylglycolato) was used in the preparation of a unique 10-borylated dibenzoborepin system (Scheme 32).388 As the search for cheaper, more environmentally friendly replacements for precious metals such as Pt, Rh, and Pd continues, Nakamura and co-workers examined the utility of iron catalysts in the diboration of alkynes.389 It was shown that a variety of internal alkynes were diborylated by B2pin2 in high yields in the presence of an iron salt, FeBr2, and a base LiOMe, as well as MeOBpin, which was observed to be required to provide the second boron moiety in the borylation reaction.387 The MeOBpin could be replaced by an alkyl halide to facilitate a carboboration reaction to obtain the monoborylated alkene instead of the previously isolated diborated product.387,389 The ability to conduct these reactions in the absence of a transition metal using specific reaction conditions has already been discussed (vide supra), but one more report that is noteworthy is the diboration of terminal alkynes with B2pin2 reported by Ogawa et al.390 This reaction could be conducted in the presence of catalytic amounts of organosulfides under photoirradiation conditions.390

Scheme 30. trans-Diboration of Propargylic Alcohols by Uchiyama et al.

3.3. Alkenes (Aliphatic)

Simple aliphatic alkenes were first diborated using B2Cl4 in 1954.80 The initial study examined the diboration of ethylene, while subsequent studies expanded the scope of these additions using tetrahalogenato diborons and provided more detail on the nature of the observed products.82,83,153,391−396 These initial reactions have recently been used as the basis of a computational study by Brown and co-workers on the simple addition of B2X4 to alkenes (see section 2.1).87 The influential work by Miyaura, Suzuki, and co-workers on catalytic diboration of alkynes found alkenes to be unreactive under identical conditions,313 due to the weaker binding ability of these substrates, preventing them from displacing the phosphine ligands of the transition-metal catalyst precursor. In an early report by Baker, Marder, and co-workers, vinyl arenes and the activated alkene allylbenzene were diborated with B2cat2 using a gold(I)/phosphine catalyst system (see section 3.3).335 Other early reports described the successful catalytic diboration of aliphatic alkenes utilizing zerovalent platinum catalyst precursors bearing only labile ligands: norbornene,316 cyclooctadiene,316 and dibenzylideneacetone.314 These initial reports included diborations of both internal and terminal alkenes with B2pin2314 and B2cat2,316 showing tolerance of ester

Fernández and Perez demonstrated that a copper(I)−NHC catalyst was capable of the catalytic diboration of alkynes with B2cat2 in refluxing THF.345,384 Subsequent computational studies helped confirm the reaction mechanism (following the general pathway outlined in Scheme 24)351 and explained the enhanced reactivity observed for B2cat2 over B2pin2.352 A later report showed that copper(I) phosphine complexes are effective catalysts for the diboration of alkynes and arynes with B2pin2.301,356,385−387 This system was also found to operate through the pathway shown in Scheme 24. Further support for this mechanism came in the form of the stoichiometric reaction of an aryl−copper species with B2pin2, which resulted in the formation of an aryl−Bpin species.356 The authors, Yoshida and co-workers, also made use of the diboration of alkynes in the preparation of two biologically active molecules (Figure 8). From this study it is noteworthy that, in contrast to the cis-1,2diboration product observed with Pt(0) catalysts, when methyl propargyl ether substrates were employed, the authors observed replacement of the methoxy group(s) of the substrate with Bpin groups, in addition to diboration of the triple bond (Scheme 31). O


Chemical Reviews

Review

Scheme 31. (a) Tetraborylation of 1,4-Dimethoxy-2-butyne; (b) Proposed Mechanism for the Tetraborylation Process

Scheme 32. Synthesis of an Unusual 10-Borylated Dibenzoborepin

group identified TADDOL-derived L1 (Figure 9) as the optimal ligand and found the reaction to be quite insensitive to

groups and chlorine atoms in the substrate. The platinumcatalyzed diboration of aliphatic alkenes follows the same general oxidative addition/reductive elimination mechanism shown in Scheme 20. These initial reports found the substrate scope to be limited to terminal alkenes and strained cyclic alkenes. Marder and co-workers also demonstrated the catalytic diboration of norbornene and styrenes (vide infra) with the zwitterionic rhodium(I) catalyst, [Rh(dppm)(η6-Bcat2)].336 Several years later, chiral rhodium(I)337,338,397,398 and platinum(0)399 catalysts were utilized with B2cat2 and B2pin2, respectively, by Morken and co-workers to effect the enantioselective diboration of internal and terminal alkenes.378,400 A later report by Toribatake and Nishiyama demonstrated the high activity and enantioselectivity of a rhodium(III)−pincer bis-acetate catalyst precursor in the diboration of terminal alkenes.401 The diborylalkanes generated from this reaction were subsequently oxidized to generate the corresponding chiral diols.400,401 Further investigations by the same group used a similar reaction to synthesize the optically active 3-amino-1,2-diols via Rh-catalyzed diboration of the respective N-acyl-protected allylamines.402 Other reports have also utilized this facile method to generate a range of 1,2diols.403−406 The resulting diborylalkanes have likewise been subjected to terminal-selective cross-coupling reactions and subsequent oxidation to generate carbohydroxylation products.403 A thorough experimental and computational study of enantioselective zerovalent platinum-catalyzed alkene diboration has been published by Morken and co-workers.407 This

Figure 9. TADDOL-derived chiral ligands for enantioselective diborations.

the platinum(0) starting material, with the optimal catalytic conditions being 1 mol % platinum and 1.2 mol % ligand.400,407 Kinetic experiments showed the reactions to be nearly zero order in B2pin2 and alkene, suggesting that the rate-determining step does not involve association or dissociation of either substrate at the platinum center. The regioselectivity of alkene insertion shown in Scheme 33 is consistent with the observed enantioselectivity, the selectivity favoring the same enantiomer as reactions of vinyl arenes (whereby a benzylic intermediate is assumed for these substrates), and with DFT calculations. Armed with a detailed knowledge of the diboration reaction, Morken and co-workers formulated a one-pot route using the diboration reaction in tandem with a Suzuki−Miyaura crosscoupling reaction to synthesize a variety of chiral allylic alcohol and amine compounds.397,400,408 Notably, this synthetic route P


Chemical Reviews

Review

Another major development came in 2011 from the Fernández group, who discovered that metal-free systems could catalyze the diboration of unactivated olefins.219,225 In this case, a combination of base and alcohol served to activate the diboron reagent to facilitate addition across the alkene C C bond (Scheme 25). An asymmetric variation of this method was subsequently published by the same group, in which chiral alcohols served to induce low to moderate levels of enantioselectivity.226 Recently, Fernández and Fujita published a report on the use of the crystalline sponge method to confirm that the metal-free diboration reaction goes through a synaddition mechanism, which supports the previously predicted mechanism, using DFT calculations.415 A number of symmetrical diboron reagents were tested, with the highest yields shown when B2pin2 was used. Fernández and co-workers also reported the ability of the mixed diboron system, BpinBdan, to diborate a range of aliphatic alkenes;219,416 however, unlike B2pin2, the same system could not diborate vinyl arenes, with only the monoborylated product being obtained. Recently, Morken and co-workers used a similar principle to facilitate the diboration of alkenes using carbohydrate-derived catalysts. It was suggested that 1,2-bonded diboronates were possible intermediates in the catalytic cycle, with these species previously discussed in section 2.5.2.417 Allylic alkenes are also susceptible to diboration by various different catalysts. In 2006, a zerovalent platinum−NHC catalyst was used in the diboration of these compounds, along with allylsulfones, using B2cat2 or B2pin2 for the preparation of 1,2-dihydroxy compounds under mild conditions.418 The same group also found that an iridium(III)based catalyst could add B2cat2 to allylic alkenes in the presence of excess NaOAc.348 Interestingly, Alonso et al. observed recently that a titania-supported platinum nanoparticle system was able to promote diborations of allylic alkenes in the absence of solvent or added ligand.364

Scheme 33. Proposed Mechanism for the Enantioselective Diboration of Alkenes

starts with nonfunctionalized, readily available terminal alkenes and is able to generate a variety of biologically active compounds (Scheme 34). The authors demonstrated that bisboryl alkanes are actually more reactive in the cross-coupling reaction than analogous boryl alkanes. The same group continued their investigations into the tandem reactions, which led to the observation that after the initial diboration the subsequent cross-coupling reaction could be directed by the presence of an hydroxy group β to the pinacol borane.409 This route was developed to generate γ-oxygenated boronates from the sequential directed diboration and cross-coupling reactions, followed by either acylation or silylation.409 The use of NHCs in exchange for phosphorus-based ligands has also been investigated. Fernández and co-workers initially observed that a silver(I)−NHC complex was competent in catalyzing the diboration of vinylcyclohexane with B2cat2,410 while several years later the same group reported that palladium(II)−NHC complexes could facilitate the diboration of terminal aliphatic alkenes and vinyl arenes.347 Contrary to the catalytic cycle proposed for platinum(0) complexes, these palladium catalysts are believed to operate through the transmetalation pathway similar to that shown in Scheme 24. Additionally, palladium and platinum complexes were later shown to be effective catalyst precursors for the diboration of cyclic alkenes,411 as well as phenyl vinyl sulfide, which was subjected to diboration with B2cat2, using Pt(dba)2.412 Bimetallic palladium(II) complexes have also been used for tandem diboration (with B2cat2) and Suzuki cross-coupling reactions of alkenes, although the mechanism for the diboration step has not been studied in detail.413,414

3.4. Alkenes (Vinyl Arenes)

The first report of catalytic diboration of vinyl arenes came in 1995 from Baker, Marder, and co-workers for 4-vinylanisole utilizing B2cat 2 and a rhodium(I) catalyst. 335 Due to competition resulting from β-hydride elimination of the benzylic intermediate (Scheme 35, bottom left), yields of the diboration product were quite low. However, a zwitterionic rhodium(I) catalyst precursor containing the dppm ligand,

Scheme 34. Synthesis of Enantiomerically Enriched Lyrica, Featuring Asymmetric Alkene Diborationa

a

RuPhos = 2-dicyclohexylphosphino-2′,6′-diisopropoxybiphenyl. Q


Chemical Reviews

Review

diborations of vinyl arenes, as well as allylic alkenes. In the case of the iridium(III) catalyst, an excess of NaOAc was required for good conversion, and modest enantioselectivity was achieved (10% ee). Dinuclear palladium(II) complexes have also been shown to catalyze not only the diboration of vinyl arenes but also the subsequent cross-coupling step.413 In addition, gold(I),419 copper(I),345 and silver(I)−NHC410,419 complexes have been used as catalysts for the addition of B2cat2 to styrene. In 2011, metal-free diboration of vinyl arenes using base in MeOH was established by Fernández et al. when they investigated the diboration reaction of a range of alkenes with B2pin2.225 They subsequently reported the metal-free diboration of indene under similar conditions in the presence of 2 equiv of chiral alcohol, B2pin2, and Cs2CO3;226 however, the conversion, chemoselectivity (diboration vs hydroboration), and enantioselectivity were poor.

Scheme 35. Proposed Mechanism for the Diboration of Vinyl Arenes

[Rh(dppm)(η6-Bcat2)], prepared from [Rh(dppm)(acac)] showed good selectivity and yield while operating under milder conditions (vide supra).336 Chiral rhodium(I) catalysts were also utilized by Fernández and co-workers and shown to be competent catalysts for the diboration of vinyl arenes with a variety of diborons; however, selectivity for the diboration product and asymmetric induction values were modest.339 Subsequent work by Toribatake and Nishiyama demonstrated that changing the catalyst to a rhodium(III)−pincer bis-acetate catalyst precursor facilitated the very rapid diboration of vinyl arenes in the presence of B2pin2 and catalytic NaOtBu.401 The same initial report by Marder and co-workers also examined gold(I) phosphine complexes as catalyst precursors.335 The gold-catalyzed reactions, while slow, proved to produce much higher yields of the desired diboration product than the initially examined rhodium(I) complex. Subsequent work by the Fernández group, examining diborations catalyzed by alternative gold(I) complexes, showed that reactions were accelerated by the introduction of excess B2cat2.346 This observation led to a more thorough examination of the reaction, which revealed that the catalytically active species in this case was in fact gold nanoparticles. As B2cat2 reduces gold(I) to zerovalent gold, excess diboron reagent accelerated the reaction. A head-to-head comparison of diboration of vinyl arenes and bis-hydroboration of aryl alkynes with rhodium(I) catalysts found that bis-hydroboration produced higher yields and increased selectivities.339 Marder and co-workers later reported the diboration of vinyl arenes using Pt2(dba)3 and chiral diborons.199 However, only low to modest diastereomeric excesses were obtained. Fernández and co-workers were able to facilitate the diboration of vinyl arenes with B2cat2 using a zerovalent platinum−NHC catalyst under ambient conditions.418 Furthermore, the same platinum(0) nanoparticles bound to a titania surface,364 the chiral iridium(III) catalyst348 and palladium(II)-NHC complex347 discussed previously (section 3.3), were able to promote

3.5. Alkenyl and Alkynyl Boronate Esters

Vinyl boronate esters are often products of diboration reactions; however, these species can also readily undergo reactions with diborons. For example, tetraborylethene is presumably an intermediate in the synthesis of a hexaborylethane from a diborylacetylene and could be isolated through modification of the reaction conditions (Scheme 36a).420,421 The diborations of these species often resulted in mixtures of products. Nishihara et al. also used alkynylboronate esters in the synthesis of gem-diboryl alkenes. The boryl acetylene undergoes diboration followed by a Suzuki−Miyaura coupling to generate the desired product (Scheme 36b).422 Marder and co-workers reported the rhodium(I)-catalyzed diboration of E-styryl boronate esters with B2cat2.423 Perhaps surprisingly, the dominant product of the reaction with several different catalysts was a 1,1,1-triborylalkane (Scheme 37), Scheme 37. Rhodium-Catalyzed Diboration of E-Styryl Boronate Esters

which was produced through a sequence of alkene insertions into the Rh−B bond and β-hydride eliminations from benzylic intermediates (see Scheme 35) following the initial insertion of the CC bond into a Rh−B bond, whereupon a final C−H reductive elimination provided the 1,1,1-triborylalkane. Recently, Zhang and Huang used the combination of cobaltcatalyzed dehydrogenative borylation and hydroboration to

Scheme 36. (a) Diboration and Bis-Diboration of an Alkynyl Bis-Boronate Ester; (b) Diboration of Borylacetylene and Subsequent Cross-Couplinga

a

mida = N-methyliminoidiacetic acid. R


Chemical Reviews

Review

Pt(dba)2 resulted in 1,2-diboration.314 Shortly thereafter, Marder, Norman, and co-workers showed that other diborons, including chiral derivatives, could be added to 1,3-dienes in a 1,4-fashion as well; however, little asymmetric induction was achieved in this manner.198 Morken and co-workers later used bulky chiral phosphine ligands, which, when added to a Pt2(dba)3-catalyzed diboration reaction mixture, produced 1,4-diols with high enantioselectivity, following oxidative workup.427−430 The bulky, electron-rich cyclic phosphine L2 (Figure 9), when added to a zerovalent platinum precursor proved to generate the most active catalyst for this transformation. The diastereoselective 1,4-diboration of 1,3-dienes has been applied as a convenient route to 1,4-diols in the synthesis of several natural products. Initially, (+)-transdihydrolycoricidine was synthesized from a readily available cyclohexadiene derivative (Scheme 39),431 while another attempted synthesis used a singlet oxygen cycloaddition reaction with the cyclohexadiene derivative; however, this route provided no diastereoselectivity.431 Morken and coworkers also utilized the enantioselective 1,4-diboration of trans-pentadiene in the synthesis of (+)-discodermolide.432 Morgan and Morken applied the product of a 1,4-diboration using a chiral diboron to induce good enantioselectivity in the next step of the reaction, wherein the boron-containing product was added to an aldehyde.433 Coordination of the aldehyde at a boron center activated the substrate toward nucleophilic attack by the π-bond, creating a new carbon−carbon bond and cleaving a carbon−boron bond, where the net result was a chiral allylboration reaction (Scheme 40). A similar reaction sequence was used to diborate dienes catalytically with a zerovalent nickel catalyst wherein the diboration product added in an intramolecular fashion to an aldehyde then to a second aldehyde, resulting in the formation of four contiguous stereogenic centers.434 Morken and coworkers studied the zerovalent nickel-catalyzed allylboration of aldehydes, finding that upon mixing the 3 substrates (diboron, aldehyde, and diene) together they obtained the complementary product to the platinum-catalyzed reaction (Scheme 41, left). However, when diene and diboron were mixed initially, products with the opposite regioselectivity were observed (Scheme 41, right).435 This finding suggests that stepwise diboration−allylboration was not occurring when all of the

synthesize a range of similar products from vinyl arenes with B2pin2.424 3.6. Dienes

An early example of diboration of dienes was reported by Haubold and Stanzl in 1979. It was observed that the reaction of B2Cl4 or B2F4 with 1,3-butadiene generated the diborated product, 1,4-bis(dihalogenoboryl)-2-butene;425 however, the product was only characterized via elemental analysis. The next study of the diboration of conjugated 1,3-dienes using zerovalent platinum catalysts was not conducted until almost 20 years later in 1996 by Miyaura and co-workers.426 The reaction of 1,3-dienes with B2pin2, catalyzed by Pt(PPh3)4 resulted in 1,4-diboration (Scheme 38a).341,426 During their Scheme 38. (a) Proposed Mechanism for the PlatinumCatalyzed Diboration of 1,3-Dienes; (b) Borylative Coupling of Isoprene

study, the authors noted that using a phosphine-free catalyst Pt(dba)2 in the reaction of B2pin2 with isoprene gave a new product, resulting from a tandem dimerization/diboration sequence. The use of 3 equiv of isoprene resulted in quantitative formation of this coupling product (Scheme 38b). The same authors later reported that, at room temperature, diboration of neoprene with B2pin2 catalyzed by

Scheme 39. Use of a Diastereoselective Diboration in the Total Synthesis of (+)-trans-Dihydrolycoricidine

S


Chemical Reviews

Review

Scheme 40. Diboration/Allylboration of a 1,3-Diene

Scheme 41. Regioselectivity in the Allylboration of 1,3-Dienes

components were added simultaneously, but the three components come together at the metal center during the reaction. Remarkably, switching the ligand to P(SiMe3)3 resulted in yet another change in regioselectivity in the nickel-catalyzed allylboration reaction (Scheme 41, bottom).436 The authors speculated that the change in regioselectivity was an electronic effect, causing the reductive elimination to occur prior to allyl isomerization at the metal center. Following the discovery of their excellent activity as aldehyde allylboration catalysts,434,435 Morken and Ely were subsequently motivated to study the activity of zerovalent nickel complexes in the diene diboration reaction.437 Catalyst systems comprising Ni(COD)2 (COD = cis-1,4-cyclooctadiene) and PCy3 were found to be highly active and stereoselective catalysts for the 1,4-diboration of 1,3-dienes. Importantly, reactions using these catalysts showed no evidence of 1,2-diboration and were effective in the diboration of internal 1,3-dienes, a class of substrates inert under platinum-catalyzed reaction conditions. However, like the zerovalent platinum systems, only dienes capable of adopting the s-cis configuration were reactive. The observation that styrene and 2-vinylnaphthalene did not undergo 1,2-diboration prompted the authors to suggest that the standard oxidative addition/insertion mechanism did not apply in this case. Instead, they suggested an alternate mechanism involving initial coordination of the diene to the nickel complex, followed by reaction with B2pin2, resulting in a nickel(II)−allyl intermediate, which generated the 1,4-diboration product upon reductive elimination (Scheme 42). Interestingly, the Morken group later reported the unexpected enantioselective 1,2-diboration of 1,3-dienes.438 The reversal in selectivity is achieved using cis-1,3-dienes or 1,1disubstituted-1,3-dienes as opposed to the trans-1,3-diene, previously employed in platinum-catalyzed dibora-

Scheme 42. Proposed Mechanism for the Zerovalent NickelCatalyzed Diboration of 1,3-Dienes

tions.198,426,428,433 The 1,2-diboration reaction was paired with a subsequent allylboration of an aldehyde in a one-pot reaction, allowing for access to a wide range of chiral diols, following oxidation. Alternatively, the terminal boronate ester could be subjected to hydrodeboronation (Scheme 43, bottom) or homologation (Scheme 43, right). The ability to generate chiral centers, stereoselectively, and even enantioselectively makes the catalytic diboration of 1,3-dienes a useful reaction in the synthesis of natural products and other biologically active molecules. 3.7. Allenes

Allenes were first shown to be competent substrates in the diboration reaction by Miyaura and co-workers in 1998.439 As with many other substrate families, diboration reactions were initially studied using B2pin2 with zerovalent platinum complexes as the catalyst precursors. Regioselectivity for monosubstituted allenes favored the internal double bond, while 1,1-disubstituted and alkoxy-substituted allenes were selectively diborated at the terminal double bond. The T


Chemical Reviews

Review

Scheme 43. Diboration and Subsequent Functionalization of a 1,3-Diene

diboration of phenylallene showed differing regioselectivity depending on the catalyst system used: for the Pt(PPh3)4 catalyst system, diboration occurred preferentially at the internal double bond, while diboration at the terminal double bond was favored for the Pt(dba)2/PCy3 catalyst system. A subsequent computational study found that the presence of an electron-withdrawing substituent on the allene generally favors diboration of the terminal double bond, while electrondonating substituents favor diboration of the internal double bond (Scheme 44a).440 A recent publication by Santos and co-

Scheme 45. (a) Three-Component Coupling Reaction of an Allene, a Diboron, and an Alkyl Iodide; (b) Proposed Catalytic Cycle for the Alkyl Iodide-Promoted Catalytic Diboration of Allenes

Scheme 44. (a) Calculated Regioselectivities for the Diboration of Monosubstituted Allenes Using Pt(PH3)2 as the Model Catalyst; (b) Diboration of Allenes with BpinBdan Using Pt(dba)3/Sphos as Catalyst

Transmetalation with diboron results in the elimination of the diboration product and regeneration of the palladium boryl iodide complex (Scheme 45b). Further support for the mechanism comes with the observation that the addition of equimolar amounts of two different diborons to methylallene afforded a nearly statistical mixture of diboration products, including different boryl substituents, which is not expected if the reaction proceeds through the B−B oxidative addition mechanism normally observed for zerovalent platinumcatalyzed diborations. Morken and co-workers developed enantioselective palladium-based catalysts for the diboration of allenes.307,342,430 In these cases, an excess of a phosphorus-based ligand was added to the reaction mixture, along with Pd2(dba)3, resulting in the generation of the active catalytic species. Simple nonchiral phosphines, PCy3, PPh2Cy, and P(NMe2)3, performed best. Chiral phosphoramidite ligands also led to excellent conversions, while the use of the bulky TADDOL-derived ligand L3 (Figure 9) provided good yields along with high enantioselectivities. Subsequent in situ addition of benzaldehyde to the diboration product followed by oxidative workup produced good yields and excellent chirality transfer to the βhydroxyketone product. In the same report, Morken and co-

workers examined the use of the unsymmetrical diboron(4), BpinBdan, instead of B2pin2, in a similar system.441 It was shown that 1,1-disubstituted alkenes underwent diboration in the presence of a Pt catalyst and SPhos to give the diborated product. It was demonstrated that there was a difference between the regioselective addition of the two boron moieties to the terminal position. In the major isomer, the Bdan moiety was transferred to the terminal position, while the Bpin group was transferred to the position at the internal sp-hybridized carbon (Scheme 44b). Alternative metal complexes were also reported for the diboration of allenes, for example, palladium(II) or zerovalent palladium complexes, along with an alkenyl- or aryliodide as cocatalysts.442 These reactions occur with complete regioselectivity, with diboration taking place exclusively at the terminal double bond. The proposed mechanism begins with the threecomponent coupling of the organic iodide, diboron, and allene. The allene−carboboration coupling product is observed in 3% yield by a GC/MS examination of the reaction mixture (Scheme 45a). Oxidative addition of the boron−iodine bond initiates the catalytic cycle, and the terminal double bond of the allene is then inserted into the palladium−boron bond. U


Chemical Reviews

Review

Scheme 46. Allylboration and Subsequent Functionalization of an Allene

Scheme 47. One-Pot Diboration and Aminoallylation (left) or Hydroboration/Cross-Coupling (right)

3.8. Carbonyls and Thiocarbonyls

workers stated that initial attempts at rhodium-catalyzed diboration of allenes suffered from poor yields, regioselectivities, and enantioselectivities.342 The synthetic utility of these reactions was illustrated further when a step in the synthesis of the complex terpenoid natural product, Solanoeclepin A, was the diboration of allenes using Pd2(dba)2, reported previously by Morken et al.443 This chiral diboration/allyl addition reaction was improved and the substrate scope expanded to include a wide variety of allenes and aldehydes.444 Aldehyde addition products could also be subjected to acetic acid,444 NaOH/I2,444 or Suzuki− Miyaura coupling reactions without the need for additional palladium catalyst (Scheme 46).444 Furthermore, Morken and co-workers used a chiral phosphine ligand along with [(allyl)PdCl]2 to execute a diboration/asymmetric allyl−allyl coupling reaction with an allyl halide, producing chiral borylated 1,5-hexadienes.445 In addition, allene diboration products were found to undergo αaminoallylation (Scheme 47, left)446 or hydroboration/crosscoupling (Scheme 47, right).447 Indeed, the diboration of allenes has helped provide access to a huge family of chiral alcohols. Despite previous computational studies suggesting the unfavorable nature of a palladium diboryl oxidative addition product,112,304,305 a recent experimental and computational study of the present palladium-catalyzed allene diborations showed that the reaction may in fact proceed via this oxidative addition step.307 The use of a mixture of D24B2pin2 and B2pin2 as the diborating agent resulted in the generation of only D24 and H24 products by electrospray mass spectrometry, indicating both boryl groups in the product came from the same B2 molecule. In contrast to zerovalent platinum systems, which showed a first-order dependence on alkyne concentration, the palladium systems seemed to show a firstorder dependence on B2pin2, suggesting that oxidative addition is the rate-limiting step for these palladium-catalyzed reactions.

One early example of the reduction of a carbonyl group by a diboron reagent is the reaction reported by Sadighi and coworkers, who showed that an (NHC)copper(I)−tert-butoxide complex could catalytically reduce CO2 to CO with B2pin2 (the oxygen atom is lost as pinB-O-Bpin).343 A DFT study by Zhao, Lin, and Marder demonstrated that this reaction is promoted by the high nucleophilicity of the boryl−copper species, which results in insertion of a CO bond into the Cu−B bond, with copper and not boron bound to the oxygen atom in the resulting intermediate.448 Boryl migration from carbon to oxygen results in the generation of a copper(I) (OBpin) species and the release of CO. Lastly, transmetalation with B2pin2 regenerates the copper−boryl species, along with O(Bpin)2 (Scheme 48). In a related reaction, sulfoxides were deoxygenated to sulfides by B2pin2 in the presence of zinc(II) triflate.449 Amine- and pyridine-N-oxides can also be reduced by B2pin2 or B2cat2,450 and pyridine-N-oxides can be reduced with B2(OH)4,451 without the need for a catalyst. Additionally, Huang and coworkers established that B2pin2 could be utilized as the reducing agent in the nickel-catalyzed reductive tetramerization of alkynes,452 while Ogoshi et al. reported that B2pin2, in the presence of NaOtBu, was used as the reductant in the coppercatalyzed reaction of trifluoromethylketone with aldehyde.453 The diboration of aldehydes with B2pin2 using a modified copper(I)−NHC catalyst at room temperature was reported by Sadighi and co-workers in 2006.344 A DFT study of the aldehyde diboration reaction revealed that it proceeds through a transmetalation pathway similar to that shown in Scheme 24.355 The boryl group attacks the carbonyl carbon acting as a nucleophile, rather than an oxophile. Notably, in the absence of diboron, the copper alkoxide Cu−OCRHBpin intermediate rearranges to the more thermodynamically favorable organocuprate Cu−CRHOBpin product. Subsequently, the same copper(I)−NHC complex was reported to catalyze the V


Chemical Reviews

Review

initially reduced to Pt(0) prior to the reaction taking place. The addition of any electron-donating reagents, including coordinating solvents, hinders the reaction significantly in an analogous fashion to that observed with alkyne diboration. It should be noted that bis(pinacolato)diboron has also been used to affect the reduction of nickel(II) to zerovalent nickel.460 Morken and Hong recently generated N-silyl aldimines from aldehydes in situ and added B2pin2 using a chiral zerovalent platinum catalyst.461 These silylimines subsequently undergo acylation, resulting in one-pot asymmetric aminoborylation of the starting aldehyde (Scheme 50).

Scheme 48. Deoxygenation of Carbon Dioxide Catalyzed by a Copper(I) Complex

3.10. Other Substrates

In addition to the 1,2-diboration of CE multiple bonds (E = C, N, O, S), a few related examples have been reported. For example, the diboration of NN bonds was first reported using dichlorodiborons RClBBClR (R = tBu, NMe2) in 1995.462 Braunschweig and co-workers reported the platinumpromoted stoichiometric and catalytic insertion of azobenzene into the B−B bond of [2]-bora-metalloarenophanes (Scheme 51, for further information see section 2.8).463 These results prompted a computational study examining the diboration of Ph−EE−Ph (E = Group 15 element) species, which found that the NN bond is more reactive than the heavier group 15 element homoatomic multiple bonds.464 In 2001, Srebnik and co-workers reported the addition of B2pin2 to diazomethane, resulting in 1,1-diboration and loss of nitrogen.465 As this reaction occurred only with the assistance of a platinum(0) catalyst, it is believed to proceed through oxidative addition of the B−B bond, followed by insertion of CH2 into a Pt−B bond and reductive elimination to give the 1,1-diborated product. Several other diazo compounds were subsequently found to undergo the same transformation (Scheme 52, right).466 The substrate scope was expanded upon by Kingsbury and Wommack in 2014 to obtain chiral tertiary boronate esters and alcohols.467 A silylene can similarly react with B2pin2 to form a diboryl silane.468 Likewise, diboryl silanes were formed from compounds bearing Si−Si double bonds, though yields are modest (Scheme 52, bottom).469 Tosylhydrazones were found to undergo 1,1-diboration with B2pin2, in the presence of a base, to isolate the monoborated product (Scheme 52, left).470,471 During investigations into the mechanism, it was discovered that 1,1-diboronates could be formed by thermal reaction of B2pin2 with the in situ-formed Ntosylhydrazone sodium salt. Due to the presence of NaH, the protonation of the 1,1-diboronate product is no longer possible because of the release of H2 upon formation of the salt.472 The reaction also can be conducted with BpinSiPhMe2 in place of B2pin2. In related chemistry, isocyanides are also found to undergo 1,1-diboration by [2]-borametalloarenophanes.473 Miyaura and co-workers reported the ring-opening platinum(0)-catalyzed diboration reactions of methylenecyclopropanes (Scheme 53, left).474 More recently, Matsuda and Kirikae reported the diboration of biphenylene, catalyzed by palladium(0) complexes (Scheme 53, right).475 The proposed mechanism involves stepwise oxidative addition of the B−B bond and the strained C−C bond, resulting in a Pd(IV) intermediate. This intermediate undergoes two reductive elimination steps to give the ring-opened diborated product and regenerate the palladium(0) catalyst. Competitive hydroboration was also observed and was in fact quantitative when Pd(PPh3)3 was employed as the catalyst precursor.

diboration of a wide range of ketones, displaying a tolerance for alkenes and esters, along with other functional groups.454 Many of the isolated products were α-hydroxyboronate esters, resulting from hydrolysis of the boron−oxygen bond during workup. Clark and co-workers expanded on these results to facilitate the formation of β-hydroxyboronate esters from the respective aldehyde by an initial Cu-catalyzed diboration followed by a Matteson homologation reaction.455 This route was found to favor the β-product over the more sensitive αproduct. The diboration of ketones to form 1,1-disubstituted and trisubstituted vinyl boronate esters was also investigated by the same group. By using an initial copper-catalyzed diboration reaction and subsequent acid-catalyzed elimination, the desired products were obtained in good yields.456 Recently, the 1,1diboration of aldehydes and ketones with the unsymmetrical diboron(4) compound, BpinBdan, has been conducted under transition-metal-free conditions by formation of a diazo intermediate.457,458 Interestingly, only a single thiocarbonyl diboration has been reported in the literature, catalyzed by [RhCl(PPh3)3].412 While other thiocarbonyl diborations were attempted, only (1R)(−)-thiocamphor underwent diboration. 3.9. Imines

An early attempt to diborate imines was reported in 1998.459 Here, rhodium catalysts were used in the reaction of B2cat2 with ketimines. Instead of the diborated product, a 1:1 mixture of Nboryleneamine and N-borylamine products was observed (Scheme 49). Scheme 49. Early Attempt To Diborate an Imine

The first successful catalytic diboration of imines emerged in 2000 from Baker and co-workers.315 Imines were diborated using B2cat2 with [PtCl2(COD)] as the catalyst precursor. However, this method only produced good yields in the case of bulky diaryl aldimines. Experimental evidence suggested that the commercially available and air-stable [PtCl2(COD)] is W


Chemical Reviews

Review

Scheme 50. One-Pot Aminoborylation of Aldehydesa

a

L = L4, see Figure 9.

3.11. Unsaturated Carbonyls

Scheme 51. Insertion of Azobenzene Into the B−B Bond of a [2]-Boraferrocenophane

While the diboration of α,β-unsaturated carbonyls is undoubtedly part of some β-borylation reactions reported later in section 4.1, where only one boryl group is retained in the product, we limit the discussion here to the rare cases where characterization of the diboration product is reported. The first report of diborations of α,β-unsaturated carbonyls came from Marder, Norman, and co-workers in 1997.478 A [Pt(PPh3)2(C2H4)] catalyst was used initially, before a bulky platinum diimine catalyst was subsequently employed in the reaction of B2cat2 or B2pin2 with α,β-unsaturated ketones, resulting in 1,4-diboration. Regioselectivity was found to be reversed for α,β-unsaturated ester substrates, which underwent 3,4-diboration (Scheme 55).479 Following hydrolysis of the Oor C-bound boron enolate intermediate, β-boryl carbonyls were isolated in each case. A computational study by Marder and Lin helped elucidate the mechanism of this diboration reaction.480 Rate-determining oxidative addition of B2pin2 occurs with a platinum diimine− substrate adduct. The axial boryl group of the distorted trigonal bipyramidal complex electrophilically attacks the sp2 oxygen of the α,β-unsaturated substrate, generating a boron enolate intermediate, with platinum bound at the 4-position. This species coordinates another substrate molecule and then undergoes reductive elimination, releasing the 1,4-diboration product. The electrophilic attack of the boryl ligand on the bound substrate is particularly interesting given the boryl ligand’s normal behavior as a nucleophile when bound to Group 11 or 12 metals such as Cu or Zn or to main group metals (Scheme 56).43,220,221 In cases where 3,4-diboration products were observed, these compounds presumably arise from a thermodynamically favored migration of the boryl group from oxygen to carbon. The relative stabilities and isomerization between O- and Cbound B−, Si−, and Cu−enolates were also examined theoretically.353 Hoveyda and co-workers have shown that copper-catalyzed and metal-free NHC-catalyzed borylations can proceed through diborated intermediates (Scheme 57).214 These species can only be observed in the absence of MeOH, which is normally present in the borylation reaction mixture. Aqueous workup hydrolyzed the boron−oxygen bond and produced the β-boryl ketone.

Scheme 52. 1,1-Diboration of Carbene-Like Substratesa

a

Tbt =2,4,6-(CHSiMe3)3-C6H2.

Scheme 53. Borylative Ring-Opening Reactions

Pyrazines can be diborated at the 1- and 4-positions by B2pin2 and other tetra-alkoxydiborons without the need for a catalyst (Scheme 54).476 This was subsequently followed by the Scheme 54. 1,4-Diboration of Pyrazine

examination of sterically hindered pyrazine derivatives in the presence of substituted 4,4′-bipyridine as an organocatalyst.477 Further mechanistic studies were conducted which showed that the catalytic cycle involved two key steps. The initial step was the reductive addition of the B−B bond to the bipyridine ligand, and the second step was the oxidative boryl transfer to the pyrazine from this intermediate to regenerate the bipyridine giving the pyrazine diboration product. X


Chemical Reviews

Review

Scheme 55. Diboration of α,β-Unsaturated Carbonyls and Subsequent Hydrolysis

development of the field warrants an up-to-date summary of progress in this area.

Scheme 56. Calculated Mechanism for the Pt-Catalyzed 1,4Diboration of α,β-Unsaturated Carbonyls

4.1. α,β-Unsaturated Carbonyls, Imines, and Related Compounds

The so-called β-borylation of α,β-unsaturated ketones was first reported by Marder, Norman, and co-workers in 1997.478 This reaction proceeds through initial diboration at the 1- and 4positions with B2cat2 or B2pin2 at 80 °C, catalyzed by 5% [Pt(PPh3)2(η2-C2H4)], followed by quenching with H2O to hydrolyze the B−O bond, leaving a β-boryl enol which rearranges to the ketone (see Section 3.10). The 1,4-diboration products were also observed. Later work expanded the substrate scope for the platinum-catalyzed borylation reaction.465 Subsequent reports by the groups of Miyaura223 and Hosomi488 demonstrated copper(I)-promoted boryl additions to α,β-unsaturated ketones, while the Miyaura group also included other Michael acceptors including α,β-unsaturated esters and nitriles. The reactions are proposed to proceed through a boryl−copper intermediate, which then attacks the electrophilic substrate.224 In the Miyaura reports, stoichiometric amounts of a base additive (potassium acetate) and CuCl were required for optimal reactivity, suggesting that coordination of the acetate anion to either the diboron or the copper complex may also be an important step. Hosomi used only catalytic amounts of CuOTf or CuCl and a tri-n-butylphosphine additive (Scheme 58). Interestingly, reactions did not proceed without the phosphine additive or when using a chelating diphosphine ligand.

Scheme 57. Diboration of α,β-Unsaturated Ketones, Catalyzed by a Copper(I) Complex, or an N-Heterocyclic Carbene

3.12. Diagram Summarizing Section 3

Scheme 58. Copper(I)-Catalyzed β-Borylation of an α,βUnsaturated Ketone

Marder and Lin studied the mechanism of these reactions and confirmed that they proceed via CC insertion into a copper−boron bond, followed by keto−enol isomerization to a copper−alkoxide species which then undergoes protonation or metathesis with B2pin2, generating the borylation product or the 1,4-diboration product, respectively.43,353 Interestingly, they note that a protic additive is vital to the borylation of methyl acrylate due to its inability to undergo keto−enol isomerization. Thus, the organocuprate intermediate, which is inert to metathesis with an incoming B2pin2 molecule,355 must be protonated by the alcohol (Scheme 59). Generally, the boron− oxygen bond of the 1,4-diboration products is hydrolyzed upon workup, and the products are typically isolated as β-borylated species. It is important to note that the overall “hydroboration” of these species using diboron reagents offers complementary regioselectivity to hydroborations with boron hydride reagents,

4. BORYL ADDITION (HYDROBORATION) REACTIONS This section will focus on reactions wherein one boryl group of the diboron is added to an unsaturated substrate while the other is sacrificed. These addition reactions are often quenched by a proton from the solvent or an additive; thus, these additions can result in net hydroboration (addition of H and B(OR)2). The hydroboration of imines and enones has already been discussed above in sections 3.9−3.11. While recent reviews and perspective articles exist for the β-borylation of α,βunsaturated compounds,45,48,68,70,218−221,228,481−487 the rapid Y


Chemical Reviews

Review

Scheme 60. (a) Borylation of α,β-Unsaturated Imines (1azadienes); (b) Asymmetric Borylation and Subsequent Oxidation of α,β-Unsaturated Sulfones; (c) Generation of Chiral Phosphine Oxide Boronates from α,β-Unsaturated Phosphine Oxides

Scheme 59. Proposed Mechanism for the Copper(I)Catalyzed Borylation of α,β-Unsaturated Carbonyls

which generate CO reduction products with boron bound to oxygen.43,486 The mechanisms for these reactions are reminiscent of the copper-catalyzed diboration reaction, shown in Scheme 24, the only difference being that, in the present case, the organocuprate intermediate is quenched by a proton from solution instead of a second boryl group. Yun and co-workers reported the copper-catalyzed β-borylation of α,β-unsaturated carbonyls,384,489−491 nitriles,489,492 phosphates,489 and even β,βdisubstituted α,β-unsaturated esters493 using CuCl and a chiral or nonchiral phosphine as their catalyst, along with a base additive. They found that the addition of a catalytic amount of base and an excess of alcohol is key to the reaction. An impregnated copper on magnetite system has also been effective for the β-borylation reaction, offering the advantage of an easily separable and reusable catalyst.494 A ligandless copper catalyst system CuCl and NaOtBu was used to perform the β-borylation of α,β-unsaturated carbonyls in water.495 The same CuCl/NaOtBu combination was employed along with chiral phosphine ligands for asymmetric copper-catalyzed borylations of unsaturated carbonyls,496−498 amides,499 and nitriles.498 Similar conditions were also used by Hall et al. to generate 1,1-diboron compounds from β-boronyl acrylates. The Bpin group was reacted subsequently to form the trifluoroborate salt and then chemoselectively cross-coupled to form benzylic or allylic boronate esters.500 Additionally, the use of a copper(0) bipyridine-based catalyst for the borylation of α,β-unsaturated carbonyls in water was reported.501 Fernández and Solé reported the copper-catalyzed βborylation of α,β-unsaturated imines (1-azadienes) using the same CuCl/base (NaOtBu, NaOAc, NaOMe, NaOH) combination along with PCy3 (Scheme 60a).502 Another report by the Fernández and Whiting groups detailed the use of Cu2O as a catalyst for the base-free β-borylation of α,β-unsaturated imines.503 A chiral copper(I) complex was also established as a good catalyst for the β-borylation of α,β-unsaturated sulfones, producing chiral β-hydroxy sulfones upon oxidation (Scheme 60b),504 while a similar system was also used to develop the first asymmetric synthesis of ambiphilic phosphine oxide boronates (Scheme 60c).505 Related asymmetric copper(I) catalyst systems for the borylation of α,β-unsaturated conjugated systems were reported by the groups of Hoveyda, 506 McQuade, 507

F e r n á n d e z , 3 9 8 , 5 0 8 − 5 1 2 M a z e t , 4 8 5 M a , 5 1 3 − 5 1 5 a n d others.496,516−521 Enantioselective borylation of α,β-unsaturated aldehydes has been employed in tandem with a Wittig reaction to provide access to homoallylboronates (Scheme 61).522 The amine cocatalyst is proposed to activate the substrate to nucleophilic attack by transiently generating a chiral iminium cation from the aldehyde group. Asymmetric copper(I)catalyzed borylation of α-dehydroamino acid derivatives was used to afford chiral β-hydroxy-α-amino acids.523 Although enantioselectivities were excellent for this reaction, an approximately 1:1 diastereomeric mixture of products was obtained. Kinetic resolution of a racemic mixture of β-borylated products through lipase-catalyzed hydrolysis or transesterification reactions has also been reported.524 Santos exploited the βborylation reaction in the synthesis of β-boryl carboxylic acids (Scheme 62a), which can be reacted with amines and hydrolyzed to generate N-terminal boronic acids, compounds which have proven to be useful protease inhibitors.525 Fernández and co-workers noted that borylation and electrophilic fluorination reactions of α,β-unsaturated ketones can be done in a one-pot fashion (Scheme 62b).526 Furthermore, Fernández and co-workers prepared γ-amino alcohols in a highly enantioselective fashion through a one-pot copper(I)-catalyzed condensation/borylation/reduction/oxidation reaction from imine starting materials.527,528 Ketones could also be subjected to the same protocol (Scheme 63). The reduction step of the borylation/reduction/oxidation sequence depicted in Scheme 63 had previously been studied by Whiting and co-workers.529 The same borylation/reduction/ oxidation sequence could be performed with α,β-unsaturated ketones.527 Fernández and Whiting also introduced four- and five-step one-pot sequences, including a borylation step, in the preparation of γ-aminoalcohols and 1,3-oxazines, respectively.530 A double asymmetric borylation method could be used to desymmetrize prochiral 1,4-Michael acceptors.531 The same groups published a report documenting the conjugate addition to unsaturated bulky aldimines, generated in situ from enals (Scheme 64). The use of chiral diphosphine auxiliary ligands led to high enantioselectivity in the borylation step. The Z


Chemical Reviews

Review

Scheme 61. One-Pot Borylation/Wittig Reaction of an α,β-Unsaturated Aldehyde

Scheme 62. (a) Preparation of β-Boryl Carboxylic Acids; (b) Borylation and Electrophilic Fluorination of α,β-Unsaturated Carbonyls

Scheme 63. One-Pot Borylation/Reduction/Oxidation Reaction of an α,β-Unsaturated Species

Scheme 65. Copper(I) Bifluoride-Catalyzed Borylation

products of these reactions could be subjected to an oxidative workup, forming chiral γ-amino alcohols, or hydrolysis, forming the chiral β-boryl aldehydes.532 Similar reactions were also conducted in an attempt to make the β-boryl aldehyde by initially converting the α,β-unsaturated aldehyde in situ into the respective imine, followed by catalytic borylation and then workup; however, the product was extremely unstable, and therefore, subsequent Wittig olefination was used to facilitate the generation of a stable and versatile homoallylic boronate ester.533 Furthermore, starting from the α,β-unsaturated aldehyde, such a process has been utilized in the total syntheses of (R)-fluoxetine and (S)-duloxetine.534 A novel copper(I) bifluoride NHC complex showed relatively high activity for the β-borylation of an α,βunsaturated ester (Scheme 65); however, a copper complex with a chiral NHC ligand used in the study showed poor yield and enantioselectivity.535 Borylations of α,β-unsaturated carbonyls using bulky copper(I) phosphine catalysts and B2(OH)4 have also been reported.536 Santos and co-workers reported the copper(I)−NHC-catalyzed β-borylation of α,βunsaturated carbonyls and nitriles by PDIPA (Figure 5).201,202,537 As expected, the three-coordinate boron center

serves as the nucleophile in the reaction and is eventually transferred to the substrate. In a surprising observation, Santos and co-workers discovered that a copper(II) chloride/amine system could catalyze the borylation of α,β-unsaturated ketones and esters in air using water as the solvent.538 Although a variety of nitrogencontaining bases were effective, catalyst systems containing 4picoline were found to provide the highest conversion in the βborylation of 2-cyclohexen-1-one. Kobayashi and co-workers simultaneously published a report with an asymmetric variation of the copper(II)/water reaction conditions (Scheme 66a).539 A similar copper system was developed for industrial applications, combining basic CuCO3 and PPh3 to catalyze the β-borylation of a range of Michael acceptors in water.540 The borylation of a selection of model alkenes and alkynes was also reported. Kobayashi et al. recently adapted their previously reported Cu(II)/water system to facilitate the boron conjugate addition using B2pin2 to α,β-unsaturated imines,541 cyclic and acyclic

Scheme 64. In Situ Generation and Borylation of Bulky Aldimines, and Subsequent Reactions of the Borylated Products

AA


Chemical Reviews

Review

Scheme 66. (a) Chiral Copper(II)-Catalyzed β-Borylation in Water; (b) Enantioselective 1,6-Boration to Synthesize Allylboronates

Scheme 67. (a) Monoborylation of Enones in the Absence of a Transition Metal; (b) Metal-Free Catalytic Hydroboration of Aldimines and Ketimines

enones,542 α,β-unsaturated esters, amides, and nitriles,542 as well as the β-borylation of α,β,γ,δ-dienones and dienoesters.543 However, for the latter report, the route was only successful if substrates disubstituted at the β-position were used. Therefore, Lam and co-workers went on to develop a system which could successfully facilitate the 1,6-boration of α,β,γ,δ-unsaturated esters and ketones without a required substituent blocking the β-position (Scheme 66b).544 Investigations into the catalytic potential of zerovalent palladium or nickel complexes in asymmetric β-borylation of α,β-unsaturated esters were conducted by Fernández, Westcott, and co-workers,545 while Oshima et al. reported a zerovalent nickel phosphine system that catalyzed the borylation of α,βunsaturated esters and amides.546 Similar reactivity has been observed with [RhCl(PPh3)3] for the borylation of α,βunsaturated carbonyls and nitriles with B 2 pin 2 and B2neop2,547 while recently a CCC−NHC pincer Rh complex was shown to quantitatively borylate α,β-unsaturated carbonyl compounds with B2pin2, with the latter used to generate products with boron-substituted quaternary carbon centers.548 Additionally, Nishiyama and co-workers reported the rhodium(I)-catalyzed enantioselective β-borylation of α,β-unsaturated ketones, esters, and amides with B2pin2.549,550 In contrast to Fernández’s palladium and nickel systems,545 the rhodium(I) catalyst showed decreased enantioselectivity with bulkier ester functionalities.549,550 The use of palladium as a catalyst for the borylation reaction was further exploited by Fernández and coworkers, who performed a tandem borylation/arylation of α,βunsaturated carbonyls with the use of a single palladium catalyst.551 Hoveyda and co-workers noted that, in contrast to many other copper catalysts, the active catalyst derived from the reaction of an NHC with CuCl and 2 equiv of NaOtBu showed high activity in the absence of MeOH.214 The authors propose the strong σ-donor ability of the ligand to be responsible for the facile release of the product from the organocuprate intermediate. The same group has shown that these conjugate additions of boryl groups can be done in the absence of a transition-metal catalyst (Scheme 67a).214,215 Instead, they utilized N-heterocyclic carbenes, generated in situ from imidazolium salts and alkoxide, as catalysts for the addition of a boryl group to α,β-unsaturated ketones. Additionally, they

used a similar NHC catalyst system to establish a novel route for the enantioselective boryl conjugate addition to enones, in the presence of a catalytic amount of base, DBU (DBU = 1,8diazabicyclo[5.4.0]undec-7-ene).552 Similar to the metal-free diboration mechanism shown in Scheme 25, coordination of the carbene to one of the boron centers dramatically increases the nucleophilicity of the other boron atom (see section 2.5.2).213−215 Additional mechanistic studies on these reactions have recently been conducted by Hoveyda and co-workers to try to gain more insight into why excess base and methanol are necessary in many of these reactions and why the reactions are selective.553 This methodology was subsequently extended to include chiral boronation of α,β-unsaturated ketones, esters, aldehydes, amides, and nitriles.554 An NHC bearing a pendant amine group was also competent as a catalyst for the borylation of α,β-unsaturated ketones.555 Likewise, an amine/NHCcatalyzed β-borylation reaction has also been applied in tandem with a Wittig reaction, allowing access to homoallylboronates.556 Sun and co-workers developed a protocol involving an NHC-precursor (imidazolium salt) and a base (DBU) in methanol for the borylation of α,β-unsaturated ketones, esters, and sulfinyl aldimines under mild conditions and open to the atmosphere (Scheme 67b).557 A similar protocol has been reported by Song, Ma, and co-workers for the enantioselective β-boration of acyclic enones.558 Fernández and co-workers applied a similar protocol in the phosphine-promoted asymmetric boronation of α,β-unsaturated ketones,559 esters,559 and tosylaldimines.230 They also examined the use of iron(II) salts as Lewis acid activators for the Michael acceptors.354 The protocol evolved further as the stoichiometric amount of base initially used is not required228 and a simple Bronsted base/alcohol system proved capable of the β-borylation reaction (Scheme 68).228 The mechanism originally proposed (Scheme 68a) has been superseded by an alternative one in which the phosphine attacks the substrate (Scheme 68b). In cooperation with Whiting, the same group established that in situ formation of [B2pin2OMe]− 232 could facilitate the asymmetric β-boration of α,β-unsaturated imines in the presence of a chiral phosphine.560 The use of alternative diboron(4) reagents has also been investigated in transition-metal-free borylations. One example established that BpinBdan could react in situ to form a similar sp2−sp3 Lewis base adduct to transfer the Bdan group to the βcarbon in the α,β-unsaturated compound,561 while another example showed that the enantioselective borylation of enones AB


Chemical Reviews

Review

Scheme 68. Proposed Mechanisms for the Phosphine-Catalyzed Borylation of α,β-Unsaturated Species: (a) Original Proposal Involving R3P Coordination to B2pin2; (b) Subsequent Proposed Mechanism

Scheme 69. Enantioselective Bis-Borylation of an Alkyne

with B2neop2 using O-monoacyltartaric acid as the catalyst could be achieved.562

then subjected to a subsequent hydroboration through a similar pathway. This reaction has been expanded to include silylalkynes384,565 and shows generally superior functional group tolerance when compared to the diboration of alkenes. Monoboration of alkynes was also of great interest with many different groups exploring the reactivity of both terminal and internal alkynes with diboron(4) compounds to form the monoborylated product.301,384,385,387,566 In 2001, Miyaura et al. investigated the addition of the proposed copper−boryl complex, discussed in section 4.1, to terminal alkynes, generating the desired alkenylboronate.224 This work has subsequently been investigated by many research groups, expanding greatly upon the initial results.224 Son and Yun introduced bulky copper(I) complexes, which showed excellent regioselectivity in the borylation of activated alkynes.567,568 They subsequently elaborated on this approach by introducing the one-pot copper-catalyzed borylation and asymmetric reduction of activated alkynes, providing an elegant route from alkynes to chiral boryl alkanes (Scheme 70).569 Furthermore, investigations into the origins of the regiose-

4.2. Alkynes

Alkynes have already been mentioned previously in section 3.2, with the diboration of these substrates shown to provide a wide variety of compounds that can be used as building blocks in many synthetic pathways. However, an excellent alternative route to 1,2-diborylalkanes is through the double hydroboration of alkynes.53,301 While this reaction is known for more common hydroborating agents such as pinacolborane (HBpin)563 and catecholborane (HBcat), 339 the same reaction can be accomplished using B2pin2 as the borylating agent. Hoveyda and co-workers reported the enantioselective double borylation of alkynes affording chiral diborylalkanes with high enantioselectivity (Scheme 69).564 These reactions were catalyzed by chiral copper(I) complexes in the presence of an alcohol. Following alkyne insertion into the copper−boron bond, the alkyl group is protonated by the alcohol. The alkoxy group is then abstracted from copper by the diboron, regenerating the copper−boryl species. The initially produced alkenylborane is AC


Chemical Reviews

Review

catalyzed synthesis of branched alkenylboronate esters, instead of the more commonly observed linear products.581 The same group also demonstrated that the regioselectivity of the coppercatalyzed borylation of internal alkynes, with the same masked diboron(4) compound, was dependent on the ligand present.582 Alternative copper sources were reported with copper(0) powder used to enable the addition of a boryl group from B2pin2 to internal and terminal alkynes in ethanol,583 while Garcia and co-workers demonstrated that magnesiasupported copper or iron oxide was capable of mediating similar transformations with terminal alkynes.363 Over the past few years, the substrate scope has been extended to incorporate many different substituted alkynes. Thioacetylenes underwent hydroboration with either HBpin or B2pin2 via copper(I) catalysis, with a similar diverging reactivity shown, as previously reported by Tsuji et al.580,584 If B2pin2 was present in the reaction, it would result in the boryl group adding at a β-position (with respect to the thioether group).584 The monoborylation of silylalkynes was carried out efficiently by both Yun and co-workers585 and by Kubota et al.,586 while silyl directing groups also facilitated the borylation of internal propargylic silylalkynes.587 Additionally, recent studies have shown the excellent reactivity of ynamides with B2pin2 to generate both α,β-disubstituted (Z)-alkenamides boronates588 and (E)-β-alkenylamide boronates.589 Interestingly, McQuade and co-workers noted that selectivity in the borylation of propargyl-substituted alkynes could be altered by modifying the steric bulk of the NHC ligand (Scheme 72).590,591 Two more recent publications have utilized copper catalysts in the borylation of unsymmetrical alkynes to synthesize a range of dideuterated β-borylated α,β-unsaturated styrenes from alkynyl carboxylic acids592 and a range of enynylboronates from the selective borylation of one carbon−carbon triple bond in conjugated diynes.593 Recently, investigations showed that slight modifications to the conditions could alter whether α- or β-hydroboration occurred. Cazin and co-workers observed that β-borylation of internal alkynes with B2pin2 could be carried out with excellent selectivity in the presence of a copper(I) NHC complex and more surprisingly in air.594 Using similar conditions and the same catalyst, α-hydroboration was observed when HBpin was used, instead of B2pin2.594 Furthermore, Prabhu et al. demonstrated that in the palladium-catalyzed borylation of terminal alkynes with B2pin2, the regioselectivity could be switched depending on the ligand present.595 Alternative metals to copper have also been established as excellent catalysts in the boryl addition reactions to alkynes. A silver(I)−NHC catalyst was shown to catalyze the β-selective

Scheme 70. Borylation and Reduction of an Activated Alkynea

a

PMHS = polymethylhydrosiloxane.

lectivity in these reactions were conducted by the same group using DFT calculations.570 Additionally, these reactions were utilized by Aggarwal and co-workers in the total synthesis of the universal mating hormone α1 from the fungus Phytophthora.571 Recently, the reaction was made more accessible by Santos and co-workers by using an aqueous Cu(II)-based catalytic system under aerobic conditions to afford β-boryl-α,β-unsaturated esters, regio-, chemo-, and stereoselectively.572 Hoveyda and co-workers used CuCl−NHC catalysts for the internal borylation of terminal aryl−, amino−, and alkoxy− alkynes,573 while Carretero and Arrayás utilized CuCl− phosphine catalysts in the highly regioselective borylation of propargyl-substituted alkynes.574,575 Their protocols proved to be tolerant of a wide range of functional groups including ethers, esters, thioethers, sulfones, amines, and alcohols. Further investigations expanded this work to show that the Cu-catalyzed borylation could be carried out in conjunction with a subsequent allylic alkylation to form a variety of trissubstituted vinyl boronates.576 Recently, the borylation of both unsymmetrical and terminal alkynes with B2pin2 was used to sample the catalytic properties of several different copper complexes. Belestkaya and co-workers reported the effectiveness of Cu(I) catalysts with diethoxyphosphoryl-1,10-phenanthrolines,577 while Prabusanker et al. investigated homoleptic copper(I) imidazoline-2-chalcogenone.578 Ma and Yuen showed that copper(I) phosphine complexes are highly selective for catalytic boryl additions to internal alkynes.579 Conversely, Tsuji and co-workers documented that the use of B2pin2/MeOH for hydroboration of internal alkynes with a copper(I) catalyst gave complementary regioselectivity, compared with the corresponding hydroboration reaction with HBpin, under nearly identical reaction conditions (Scheme 71).580 The authors postulated the formation of different active catalysts, depending on the borylation agent used (L−Cu−H for HBpin and L−Cu−B for B2pin2) to be responsible for the divergent reactivity. Furthermore, Yoshida and co-workers went on to establish that BpinBdan could be used in the copper(I)-

Scheme 71. Divergent Regioselectivity in Copper-Catalyzed Hydroborations with HBpin and B2pin2

AD


Chemical Reviews

Review

Scheme 72. Ligand Effect on the Regioselectivity of the Copper(I)-Catalyzed Borylation of Propargyl-Substituted Alkynes

hydroboration of a range of terminal alkynes as well as several internal alkynes and allenes with B2pin2.596,597 Magnetically separable iron nanoparticles or ferric chloride also catalyzed a similar transformation with terminal alkynes.598 It was observed that the catalyst could be recovered by using an external magnetic field, with the catalysts reused at least 6 times without a major effect detected on the catalytic activity.598 Recently, Takita, Uchiyama, and co-workers published a report detailing the zinc(II)-catalyzed borylation of alkynes and arynes in the presence of NaOtBu.599 Alternatively to quenching the reaction with water, which generated the borylation product, the boryl− zinc addition products could be quenched with allyl bromide or iodine, resulting in allylboration or iodoboration, respectively. Transition-metal-free borylation of alkynes has also been reported. Sun and co-workers observed the borylation of terminal and internal alkynes using an NHC-precursor/base combination with methanol, which was effective for the reaction under mild conditions and open to the atmosphere.557 Song and Yang generated alkylboronates from arylacetylenes or vinyl arenes with B2pin2 under similar conditions.600

Scheme 73. Asymmetric Borylation of 1,1-Disubstituted Alkenes

Recently, the copper-catalyzed borylation of terminal olefins, in the absence of a ligand, has been investigated further to establish that different selectivity is observed depending on the substrate.609 When allyl arenes are present in the reaction, the Markovnikov alkylboronate product is detected; however, the opposite regioselectivity is observed if a styrene derivative is used.609 Similar products were also detected in the ferrous chloride-catalyzed hydroboration of aryl alkenes.610 Additionally, a copper-catalyzed borylation of these substrates was combined with an ortho-cyanation reaction followed by a silvercatalyzed cyclopentannulation to form a range of indanones.611 The borylation of strained alkenes was also explored by several groups. Tortosa reported a novel copper-catalyzed borylation of cyclopropenes to afford cyclopropylboronates, enantio- and stereoselectively (Scheme 74).612 The reaction scope was extended further by investigating the hydroboration of benzonorbornadienes and other analogous strained alkenes with B2pin2 in the presence of a copper catalyst.613 The same group also established that if MeOH was exchanged for MeI

4.3. Alkenes

Borylation reactions of alkenes are also known.566,591 Stoichiometric hydroboration reactions of B2H6 with olefins were shown to work successfully by Brown in 1957,601 while Sadighi and co-workers were able to isolate a copper(I) boroalkyl species resulting from alkene insertion into a copper−boron bond.351,602 However, interest into this particular copper-catalyzed hydroboration reaction with diboron(4) compounds increased following Hoveyda and coworkers’ publication in 2009, in which they reported the asymmetric β-borylation of vinyl arenes catalyzed by copper(I)−NHC complexes and NaOtBu in the presence of 2 equiv of methanol.603,604 This approach was applied to 1,1-disubstituted vinyl arenes, the hydroboration products of which are otherwise difficult to synthesize with good enantiopurity (Scheme 73).605 The same group expanded upon this work by establishing that under similar conditions, aryl- and alkyl-substituted vinylsilanes could undergo borylation to form a range of borosilanes.606 A similar system was recently used to examine the catalytic viability of dinuclear Cu(I) complexes and silver analogues in the hydroboration of styrene.607 The β-borylation of vinyl arenes and 1-hexene was also observed in the presence of a copper/magnetite catalyst, albeit sluggishly.494 Deng, Zeng, and co-workers developed a mild and efficient hydroboration reaction for aryl alkenes with B2pin2 in methanol using Cu2O and PPh3.608

Scheme 74. Diastereo- and Enantioselective Hydroboration of Cyclopropenes

AE


Chemical Reviews

Review

Scheme 75. Regioselective Copper-Catalyzed Borylation of Enynes

Scheme 76. (a) Differing Regioselectivity in the Borylation of Allenes, Based on the Size of the NHC Ligand; (b) OlefinDirected Borylation of Allenes

Scheme 77. (a) Borylation and Generation of Alcohol Trifluoroborate Salts from Aldehydes and Their Subsequent Protection and Suzuki−Miyaura Coupling Reaction; (b) Enantioselective Copper-Catalyzed Borylation of Aldehydes To Afford αAlkoxyorganoboronate Esters

et al. reported similar investigations into the same coppercatalyzed borylation of p-quinone methides; however, the use of a different ligand enabled them to expand the reactivity scope and improve the enantioselectivity of the reaction.616

then a successful carboboration reaction would be carried out (these types of reactions are discussed further in section 5.1).613 An enantiodivergent hydroboration was reported for similar substrates, catalyzed by a copper salt and (R,R)-Taniaphos.614 When B2pin2 was present in the reaction, the (S)-enantiomer was generated; however, the opposite was obtained when HBpin was used.614 As an interesting aside, borylative addition of Bpin to the electron-deficient alkenes, p-quinone methides, was facilitated by an enantioselective copper catalyst to generate the optically active gem-diarylmethine boronates.615 Subsequently, Tortosa

4.4. Dienes, Enynes, and Allenes

Ito and co-workers studied the asymmetric copper(I)-catalyzed borylation of cyclic 1,3-dienes and found that the regioselectivity of the reaction could be altered through modification of the reaction conditions.617 The same group demonstrated that 1,3-enynes could be borylated with high regioselectivities,618 but this selectivity was dependent on substrate structure. When AF


Chemical Reviews

Review

Scheme 78. Borylation as Part of the Total Synthesis of Bortezomib (Velcade)

catecholborane generated in situ produced the reduced Nborylamine. A computational study supports the proposed mechanism and suggested that less bulky substrates may favor diboration in the rhodium-catalyzed reaction.630 Sulfinyl aldimines were borylated in a diastereoselective fashion with B2pin2 and a copper(I)−NHC catalyst.631 This reaction was exploited for the preparation of Bortezomib (Velcade), a boronic acid-containing protease inhibitor approved for the treatment of cancer (Scheme 78).632,633 Similar copper-catalyzed borylation reactions of N-sulfinyl aldimines and ketimines in the presence of NaH and a catalytic amount of a carbene precursor were reported.634 This protocol is faster and proceeds under milder conditions than the previously reported procedure.631 A later report showed that Ntert-butyl sulfinyl imines could be stereoselectively borylated with B2pin2 using low loadings of a copper(II) catalyst formed in situ from CuSO4 and an added ligand in the presence of a catalytic amount of base in a 5:1 toluene:water solution in air.635 Aldimines could be borylated asymmetrically using B2pin2 and a catalyst derived from CuCl, NaOtBu, and a bulky chiral imidazolium salt NHC precursor,636 while Liao and coworkers established that a boryl group could be selectively added to N-Boc-imines in the presence of CuCl and a chiral sulfoxide−dialkylphosphine ligand, affording α-aminoboronate esters with high enantioselectivities.637 Furthermore, Nphosphinylimines were shown to undergo successful coppercatalyzed enantioselective electrophilic borylation to form the desired α-aminoboronate ester required in an alternative pathway to Bortezomib (Velcade).638 Sun and co-workers reported a metal-free variation of the reaction using an NHC precursor/base combination in methanol (for more information see section 4.2).557 Finally, Tang and co-workers also established that α-aryl amides can undergo hydroboration using rhodium catalysts to synthesize novel chiral α-amino tertiary boronate esters.639

the alkene functionality is monosubstituted, borylation took place selectively at the terminal alkene carbon. In cases where the alkene functionality is more sterically hindered, catalyst selection was extremely important for the regioselectivity of the addition (Scheme 75). As an interesting aside, Ito and coworkers used a similar copper(I) catalytic system to generate a range of enantioenriched heterocycles from the borylative dearomatization of indoles.619 Copper(I) phosphine-catalyzed borylations of aryl allenes have been reported to be moderately regio- and stereoselective, with the addition taking place at the terminal double bond and the boryl group ending up on the central carbon of the allene functionality.620 In the presence of a monodentate ligand, such as P(C6H4OMe-p)3, the reaction occurred at the more substituted CC bond, while bulkier bidentate ligands caused a reversal in regioselectivity, with the more hindered internal double bond undergoing borylcupration (and subsequent protonation by MeOH). Hoveyda and co-workers also noted that there was a trend of catalyst selectivity based on the steric bulk of the carbene used in the borylation of allenes (Scheme 76a).621 It was observed that with bulky NHC ligands, the internal double bond underwent the addition, while with smaller variants, the addition took place at the terminal double bond. Further work by the same group extended the substrate scope of the borylation of 1,1-disubstituted allenes to afford the alkenyl boronate esters, resulting from addition to the internal double bond, with the boryl group added to the central carbon of the allene in high enantioselectivity.622 Similar trends based on ligand size were noted by Tsuji and co-workers for the borylation of allenes and dienes.623 Additionally, they went on to report on a related system which generates useful 2-boryl1,3-butadiene building blocks efficiently via the coppercatalyzed reaction of α-alkoxy allenes with B2pin2.624 Amidesubstituted allenes have also been borylated via a coppercatalyzed route in a highly regio- and stereoselective fashion,625 while a similar catalytic system was used to facilitate the enantioselective borylcupration of allenylsilanes.626 Furthermore, a regio- and stereoselective palladium-catalyzed hydroboration of allenes using an olefin as a directing group has been reported by Bäckvall and co-workers (Scheme 76b).627

4.6. Ring-Opening Reactions

Lithium salts of epoxides can undergo stereoselective ring opening with B2pin2.640 Remarkably, reaction of the same lithium salt with BpinSiPhMe2 produced the opposite stereoisomer (Scheme 79). These reactions demonstrate an efficient way to construct elaborate CF3-containing organic molecules which would otherwise be difficult to access. A copper(I) catalyst was found to be effective for the ring opening of α,β-unsaturated epoxides, allowing for the

4.5. Aldehydes and Imines

Simple aldehydes could be borylated in methanol by a copper(I) catalyst as part of an approach to prepare chiral secondary alcohols (Scheme 77a).628 Protection of the alcohol group of the trifluoroborate salt followed by Suzuki crosscoupling afforded the corresponding benzyl ethers. Ito and coworkers went on to develop this reaction to establish a novel enantioselective copper-catalyzed borylation of the CO bond in aliphatic and aromatic aldehydes with B2pin2 to afford αalkoxyorganoboronate esters (Scheme 77b).629 Monoborylated products have also been isolated from the rhodium-catalyzed reaction of B2cat2 with ketimines (Scheme 49).459 These reactions produce a mixture of N-boryleneamine and N-borylamines through a selective β-hydride elimination step. Subsequent hydroboration of the imine with the

Scheme 79. Ring Opening of a Lithium Epoxide

AG


Chemical Reviews

Review

Scheme 80. Borylative Ring Opening of α,β-Unsaturated Cyclopropanes, Epoxides, and Aziridines

none-containing enynes,665 and dienynes (Scheme 81).666 A recent publication by Bäckvall et al. should be noted as chiral

diastereoselective synthesis of complex syn- and anti-1,4diols.641 A palladium pincer complex has been utilized by Szabó and co-workers in the borylative ring opening of substituted vinylcyclopropanes and vinyl aziridines with tetrahydroxydiboron (Scheme 80a),642 while recently the same group demonstrated that allenyl boronates and alkenyl diboronates could be generated from the copper-catalyzed borylative ring opening of propargyl cyclopropane, epoxide, aziridine, and oxetane.643 Similar nickel-catalyzed ring-opening reactions of vinylcyclopropanes644 and aryl cyclopropyl ketones645 have also been reported. Borylative ring opening can occur when α,β-unsaturated aziridines and epoxides are reacted with B2pin2 in the presence of a zerovalent nickel catalyst (Scheme 80b).646,647 Recently, Fernández and coworkers reported metal-free borylative ring-opening reactions of epoxides and aziridines with an in situ formed methoxybis(pinacolato)diboron adduct (Scheme 80c).219,229,232 The allylic boronate was isolated in good yield with subsequent oxidation to the trans-diol or reaction with benzaldehyde to generate a 1,3-diol.229,647

Scheme 81. Borylative Cyclizations of (a) Allenynes, (b) Enallenes, (c) Enynes, (d) 2-Alkynylarylisocyanates, and (e) 2-Alkynylanilines

4.7. Borylative Cyclizations and Related Intermolecular Reactions

In related chemistry, Càrdenas and co-workers presented a borylative cyclization reaction of 1,6-enynes catalyzed by palladium(II) complexes.648 The reaction proceeds in a similar fashion to the borylation reaction, but here the preorganization of the substrate by palladium results in the formation of a new carbon−carbon bond. Reductive elimination subsequently affords the borylative cyclization product. A similar intramolecular borylative cyclization reaction was observed for allenyl ketones,649 2-alkynylaryl isocyanates,650 a 2,3-dienylbutadienamine,651 2-alkynylanilines,652 enynes,648,653,654 enediynes,655,656 allenynes,657,658 enallenes,659−661 2-alkenylphenylisocyanides,662 1,7-enynes,663 enone diones,664 cyclohexadie-

phosphoric acids were used as a cocatalyst with Pd(OAc)2 to help facilitate the enantioselective cyclization taking place, which generates borylated carbocycles in high enantiomeric excess (Scheme 81b).661 In a reaction analogous to the transition-metal-catalyzed allylboration of carbonyls,434,438,667,668 the borylative coupling AH


Chemical Reviews

Review

Scheme 82. Boracarboxylation of Alkynes Catalyzed by a Copper(I)−NHC Complex

Scheme 83. Borylstannylation of Diphenyl Acetylene (right) and α,β-Unsaturated Esters (left)

Scheme 84. Aminoboration of (a) trans-β-Methyl Styrene and (b) Unactivated Terminal Alkenes

Scheme 85. Enantioselective Multicomponent Reaction Reported by Hoveyda et al.

of alkynes with α,β-unsaturated ketones was catalyzed by a nickel(0) phosphine complex.669 Hoveyda and co-workers were also able to apply their metal-free boryl addition methodology to the coupling of α,β-unsaturated ketones with benzaldehyde,214,215 while a copper-catalyzed version of the borylative reaction has also been published.670 Furthermore, Ito et al. reported the copper-catalyzed exo-borylative cyclization of alkenyl aryl ketones to obtain syn-1-aryl-2-(borylmethyl)cyclobutanol products with good selectivity.671 Borylative coupling has been accomplished using alkynes, carbon dioxide, and a copper(I) N-heterocyclic carbene catalyst, the net result being the boracarboxylation of an alkyne (Scheme 82).672 This route provides access to highly functionalized alkenes using readily available, affordable starting materials.

BpinBdan, is used instead of B 2 pin 2 , the inverse in regioselectivity is observed, with the Bdan moiety present instead of the Bpin, in the desired product.674 Borylstannylation of activated alkenes was also conducted, under similar conditions, to form a simple route to obtain a range of vicborylstannylalkanes (Scheme 83, left).384,675 Furthermore, Liao and co-workers went onto establish the synthesis of chiral organostannanes from a range of different vinyl arenes in the presence of copper(I) chloride and a chiral sulfinylphosphine ligand.676 At a similar time, Miura and co-workers introduced a method for aminoborylation of alkenes, wherein the amine acts as the electrophile and the boryl group serves as the nucleophile.677 This methodology is accomplished through the use of Obenzoyl-N,N-dialkylhydroxylamines as electrophiles and bis(pinacolato)diboron along with a copper(I)−phosphine catalyst (Scheme 84a). This method has since been extended to include methylenecyclopropanes678 and was also adapted to enable stereoselective aminoboration of bicyclic alkenes, including oxa- and azabenzonorbornadienes.679 It was observed that some of the amino-borated products were very reactive when Bpin was the boryl substituent. Therefore, B2pin2 was exchanged for BpinBdan and the reactions were carried out

4.8. Boron-Element Additions Across Mutiple Bonds

A catalyst system derived from copper(II) acetate/PCy3 has been used to effect the borylative coupling of alkynes with tin alkoxide species, resulting in a net borylstannylation (Scheme 83, right).386,387,673 These boryl stannane products could be subjected to successive Stille and Suzuki coupling reactions, allowing for the synthesis of a wide variety of substituted alkenes. Interestingly, if the masked diboron(4) reagent, AI


Chemical Reviews

Review

Scheme 86. (a) Three-Component Coupling of an Alkene, B2pin2, and Benzyl Chloride; (b) Carboboration of Alkynes Reported by Brown et al.; (c) Alkylboration of Alkenes Controlled by the Ligand Present in the Copper-Catalyzed Reaction

5. BORYL SUBSTITUTIONS Nucleophilic boryl groups derived from diborons have been shown to displace a wide variety of leaving groups from various substrates. These substitution reactions can involve the formation of a new B−C bond in combination with the loss of a leaving group. This section also covers the somewhat more complex but incredibly useful substitutions of aryl C−X functionalities.

successfully under the same conditions, affording products containing the masked boryl moiety Bdan that were easier to handle.679 Furthermore, unactivated terminal alkenes have been established as excellent substrates in the copper-catalyzed aminoboration reaction.680 It was noted that when a xantphosbased copper catalyst was used, one regioisomer was observed, while in the presence of an NHC-based IPrCuBr catalyst and BpinBdan, the opposite regioisomer was formed (Scheme 84b).680 Different three-component transformations have also been applied to other synthetic pathways. Hoveyda and co-workers reported that 2-Bpin-substituted homoallylic alkoxides could be formed in a one-pot synthesis from the reaction of B2pin2, allenes, and aldehydes or ketones.681 Subsequently, they applied the same concept to combine 1,3-enynes, aldehydes, and B2pin2 in the presence of copper(I) chloride and a chiral bis-phosphine complex to form a 1,3-diol after oxidative workup (Scheme 85).682 Recently, Procter et al. demonstrated a similar copper-catalyzed borylative cross-coupling reaction between allenes, B2pin2, and imines to afford branched α,βsubstituted-γ-boryl homoallylic amines, regio-, chemo-, and diastereoselectively.683 Lam and co-workers investigated the copper-catalyzed borylative couplings of vinylazaarenes, B2pin2, and N-Boc imines to form the boronic ester initially, before subsequent oxidation to generate azarene-containing amino alcohols.684

5.1. Coupling Reactions

The coupling reactions and cyclizations discussed in this section involve the elimination of a leaving group, as opposed to coupling reactions discussed in section 4.8.385,387 The utility of combining borylation and coupling reactions, resulting in net carboboration, was highlighted in 2000 by Cheng and coworkers in the palladium-catalyzed borylative coupling of allenes with acid chlorides.685−687 A decade later, both Tortosa’s and Yoshida’s groups reported their investigations into the copper(I)-catalyzed borylative coupling of alkynes 688,689 or alkenes 688 with alkyl halides (Scheme 86a).385−387,566 Yoshida went on to expand this work by reporting the carboboration of disubstituted alkenes and extending the different carbon electrophiles that could be utilized in the reaction, such as sterically congested 2,4,6triisopropylbenzyl chloride and 1-naphthylmethyl chloride, as well as methyl iodide and cyclopropylmethyl bromide.386,690 Brown et al. expanded the repertoire of these reactions when his group showed that a similar system could be applied to facilitate the carboboration of alkynes and allenes with aryl iodides and B2pin2 to synthesize a range of vinyl boronate esters (Scheme 86b).691 Furthermore, Fu, Xiao, and co-workers established that changing the ligand altered the regioselectivity of the copper-catalyzed carboboration reaction between alkenes, alkyl halides, and B2pin2 (Scheme 86c).692 If a combination of CuCl and Xantphos was used, the antiMarkovnikov product was obtained; however, if Cy-Xantphos was used, the slight change in ligand facilitated the formation of the Markovnikov product.692 Cooperative palladium and copper catalytic systems were also shown to be very useful in several different carboboration reactions of alkenes. Nakao and Semba reported the arylboration of vinyl arenes and methyl crotonate with B2pin2 and a range of aryl halides to obtain 2-boryl-1,1-diarylethanes

4.9. Diagram Summarizing Section 4

AJ


Chemical Reviews

Review

Scheme 87. (a) Borylative Cyclization with Phosphate Elimination; (b) Borylative Coupling Using Allenes, B2pin2, and Allyl Phosphates

and an α-aryl-β-boryl ester,693 while Brown et al. used the synergistic catalytic system to couple alkenes and B2pin2, under high levels of diastereocontrol, with either aryl or vinyl bromides 694 or 1,2-disubstituted styrenes.695 This was expanded on further by Liao and co-workers to discover the first example of catalytic enantioselective intermolecular allyboration of styrenes with B2pin2 and allyl carbonates.696 Very recently, the arylboration of bicyclic alkenes was reported, continuing the growing number of groups investigating these remarkable synthetic pathways to multifunctionalized alkenes.697 In these reactions, an alternative route to β-aryl alkylboronates was observed involving a palladium-catalyzed arylboration of norbornene or norbornadiene with B2pin2 and a range of aryl bromides or iodides.697 Intramolecular versions of this reaction have also been reported, resulting in cyclizations.566,698 Ito and co-workers examined the copper-catalyzed reaction of allylic phosphates with B2pin2, resulting in boryl addition, cyclization to give a 3membered ring, and elimination of the phosphate group (Scheme 87a).699 The reaction is believed to proceed through a borylcuprate intermediate, with the CC bond of the substrate inserting into the copper−boron bond, followed by an intramolecular nucleophilic substitution of the organocuprate for the phosphate group. More recently, Tsuji et al. reported the borylative allyl−allyl coupling of allenes with B2pin2 and allyl phosphates under similar conditions (Scheme 87b).700 It is proposed that an allyl copper species generated in the reaction reacts with the allyl phosphate present to form various boryl-substituted 1,5-dienes.700 This combination of reagents was also utilized by Hoveyda and co-workers to synthesize trisubstituted chiral alkenes initially, before using the methodology as part of the total syntheses of both rottnestol and herboxidene.701 Furthermore, the conditions were adapted to build a new subset of reactions to facilitate the carboboration of alkynes with B2pin2 and allyl phosphates to obtain a range of boron-substituted 1,4-dienes.702 In 2015, Ito and co-workers reported further borylative cyclizations by using silicon-tethered alkynes to facilitate an intramolecular alkylboration, in the presence of a copper catalyst to obtain a range of cyclic alkenylboronates (Scheme 88a).703 An interesting report by Eycken et al. combined a Heck and borylation reaction to provide a synthetic route to indolinone-3-methyl boronate esters, which could overcome several hurdles, such as the direct Miyaura reaction of the product of the hydroarylation of the alkene (Scheme 88b).704 Two reports have recently been published which demonstrate that similar reactions can be conducted to carry out either a

Scheme 88. (a) Alkylboration of Alkynes to Form Cyclic Alkenylboronates with Excellent Regio- and syn-Selectivity; (b) Domino Heck/Borylation Route To Form Indolinone-3methyl Boronate Esters

copper-catalyzed oxyboration of unactivated terminal alkenes705 or a cascade reaction with an initial borylation reaction followed by an ortho-cyanation and then a Cope rearrangement to give the desired product.706 A similar cascade reaction has also been reported for the synthesis of 1,2-bisfunctionalized arenes via the borylation and ortho-amination of aryl iodides.707 5.2. Allylic and Propargylic Substitutions

Allylic acetates can be displaced through nucleophilic attack by a boryl group in a palladium-catalyzed borylation reaction, although in the initial report allyl−allyl coupling was also observed (Scheme 89a).708 The reaction is, nonetheless, synthetically useful, as the addition of an aldehyde or imine to the reaction mixture results in near quantitative yields of the allylboration product and no allyl−allyl coupling, as the borylation product is consumed as it is generated.709 The use of a chiral diboron source allowed for moderate enantioselectivity,710 while a more recent publication reported the use of zerovalent nickel or palladium(II) catalysts in the same reaction.711 Borylation of oxo-2-alkenyl acetates resulted in the generation of oxo-2-alkenyl boranes, which can undergo an intramolecular cyclization reaction (Scheme 89b).712 Conjugate additions resulting in the displacement of an acetate have also been shown to occur using unsaturated acetates.713 These products can be converted in situ to benchstable trifluoroboronates or added to an aldehyde, resulting in allylboration (Scheme 90).714,715 The use of a chiral diboron or a chiral auxiliary group resulted in low degrees of enantioselectivity. Copper(I)-catalyzed conjugate additions of boryl groups to allyl carbonates are also possible, including asymmetric variants, resulting in elimination of the carbonate group and the generation of an enantiomerically enriched allylboronate AK


Chemical Reviews

Review

Scheme 89. (a) Palladium-Catalyzed Substitution of an Allylic Acetate for a Boryl Group; (b) Cyclization of Oxy-2-Alkenyl Acetates via Boryl Group Substitution

Scheme 90. Allylboration via Boryl Group Substitution

Scheme 91. (a) Reaction of Allylacetates with B2pin2, Followed by Allylboration and Oxidation; (b) Copper-Catalyzed Borylation of Propargylic Carbonates To Synthesize Multisubstituted Allenyl Boronates

product.716−718 A more user-friendly system was subsequently reported involving catalytic CuCl and stoichiometric NaOtBu along with an auxiliary ligand, instead of a catalytic amount of CuOtBu, which is difficult to handle due to its extreme sensitivity to air and moisture.719 A palladium-catalyzed variation of this reaction was used in the total synthesis of the Phytophthora universal mating hormone α1 (section 4.2).571 Additionally, aldehydes have been added to the reaction mixture, allowing for one-pot asymmetric desymmetrization of meso-2-alkene-1,4-diols and generation of asymmetric homoallylic alcohols (Scheme 91a).720 Recently, Ito, Sawamura, and co-workers extended this work in a novel approach to form α-chiral linear or carbocyclic (E)-(γalkoxyallyl) boronates via the borylation of allyl acetals with B2pin2.721 A reversal of regioselectivity was observed with γ-silylated allylic carbonate substrates due to a favorable interaction between the organocuprate and the silyl groups.722 The reversal in regioselectivity leads to an intramolecular cyclization, producing cyclopropane derivatives. Nucleophilic attack by a boryl group on (E)- and (Z)-homoallylic sulfonates also leads to a stereoselective intramolecular cyclization reaction, which can even produce cyclobutane derivatives.723 Additionally, propargylic carbonates were investigated by Ito and co-workers in a similar system to obtain allenyl boronates in good to excellent yield (Scheme 91b).724 The utility of these substrates was further investigated by Szabó and co-workers for the synthesis of allenyl and propargylic boronate esters.725 By using a combination of Pd and Cu or Pd and Ag in the absence of a strong base, an allenyl boronate could be obtained stereoselectively via an SN2′ mechanism, while the formation of propargylic boronate esters was observed when the copper salt was exchanged from CuI to CuCl.725 The same group went on to extend the reactivity of the reactions by incorporating the

borylation of allenes with a coupling reaction between propargyl carbonates and aryl iodides. It was postulated that the cross-coupling proceeds through an alkenyl boronic acid intermediate.726 Allyl chlorides and acetates can be displaced with a boryl group in a palladium-catalyzed reaction with B2pin2.30,31,711 Allyl boronates prepared in this fashion have been used for the development of a new allyl−propargyl coupling reaction to prepare 1,5-enynes.711 Furthermore, 1,6-enynes have also been synthesized by the borylation of allylic carbonates containing an additional alkyne group.654 If Pd(OAc)2 and an NHC, IMesHCl, is used, the reaction will form the desired 1,6enyne; however, if the ligand is changed to PCy3 then an unprecedented borylative cyclization reaction is observed, which is similar to the cyclization reactions discussed previously (section 4.7.)654 Ito, Kunii, and Sawamura published a report on the enantioconvergent synthesis of substituted cyclic hydrocarbons.727 A racemic mixture of a starting material reacted with B2pin2 in the presence of a chiral copper(I) catalyst. The chiral catalyst promotes facial selectivity, resulting in excellent enantioselectivity in the product (Scheme 92). Alternatively, benzaldehyde could be added to the reaction mixture, resulting in an asymmetric allylboration reaction. McQuade and co-workers used a similar concept, working with their bulky copper(I)−NHC catalyst to promote facial Scheme 92. Enantioconvergent Synthesis of Cyclic Boronate Esters

AL


Chemical Reviews

Review

Scheme 93. Stereoconvergent Synthesis of Boryl Alkenes through Phenolic Substitution

Scheme 94. (a) Boryl Substitution of Allylic Alcohols Catalyzed by a Palladium(II)-Pincer Complex; (b) Further Reactivity of the Initially Synthesized Allyl Boronates; (c) Borylative Substitution of an α,β-Unsaturated Alcohol and Ring-Closing Metathesis

selectivity in the borylation of E/Z mixtures of allyl aryl ethers, eliminating the phenoxy group in the stereoconvergent synthesis of chiral allylboronates (Scheme 93).728 The mechanism was subsequently studied in more detail, and a primary kinetic isotope effect was observed for MeOH, consistent with a transition state involving a proton transfer from methanol to the aryloxy leaving group.729 Furthermore, the same system was used in the first step of the asymmetric reaction to synthesize, selectively, the syn- or anti-1,2-diols.730 Szabó and co-workers discovered that a boryl group from B2(OH)4 or B2pin2 substituted for allylic alcohols in a palladium-catalyzed reaction (Scheme 94a and 94b).731−734 The authors found that the solvent mixture was key to promoting the reaction. Some methanol is required for high yields and activity, but too much methanol resulted in decomposition of the substrate, suggesting a mechanism involving the alcohol. In some cases the authors added a catalytic amount of acid to promote the reaction. Further

experimental studies revealed that transmetalation of B2pin2 with a palladium(II) allyl intermediate is shown to be slow and to proceed with high stereoselectivity, while the reductive elimination step to afford the allyl−Bpin product is fast.735 The generation of allylboronic acids in this fashion can be further exploited in the synthesis of homoallyllic alcohols through allylboration of α-amino acids via a 4-component coupling reaction.732 Using a SCS−palladium(II) pincer complex for the same reaction, the authors discovered that different solvent mixtures can result in a complete reversal of regioselectivity (Scheme 94b).736 This was rationalized by further rearrangement of the alkoxyborate species in the absence of methanol (this species reacted readily with methanol). Thus, allyl boronates generated could also be coupled with hydrolyzed acetals resulting in regio- and stereochemically pure homoallyllic alcohols.737 The allylboration of unsaturated aldehydes or acetals left two carbon−carbon double bonds in the product, which could undergo ring-closing metathesis using a Hoveyda− AM


Chemical Reviews

Review

Grubbs catalyst (Scheme 94c).738 This was expanded to incorporate ketones by initial synthesis and isolation of allyl boronic acids from allylic alcohols and B2(OH)4 followed by reaction with a range of ketones at ambient temperature in THF or CHCl3.739 In 2016, a transition-metal-free borylation of tertiary allylic alcohols was reported by Fernández and Szabó.740 It was postulated that the Lewis base−acid adduct [B2pin2OMe]− once more played an important role in the allylic borylation reaction (vide supra). Interestingly, they also demonstrated that under specific conditions, 1,2,3-polyborated products were generated through tandem allylic borylation and diboration reactions.740

step taking place and therefore was not as affected by the steric hindrance present in the substrate.749 In 2009 Marder, Steel, Liu, and co-workers demonstrated the first copper-catalyzed borylation of primary and secondary alkyl halides and tosylates for boryl groups using diboron(4) compounds.750 The reaction of 1-bromo-6-chlorohexane showed selective substitution of the bromide using 1.5 equiv of B2pin2, while 3 equiv along with slightly more harsh reaction conditions and NBu4I yielded the bis-borylated product. Interestingly, the authors note that 6-bromohex-1-ene singularly underwent borylative cyclization rather than substitution (Scheme 96b). Nearly simultaneously, Ito and co-workers published similar results with a chiral copper(I) catalyst system, which afforded high diastereoselectivities in some cases.751 Ito went on to report that alkyl halides bearing terminal carbon−carbon double bonds could undergo selective boryl substitution.752 It was observed that by altering the catalytic system for this reaction, the selectivity of the reaction could be changed from borylative cyclization previously observed698 (section 5.1) to boryl substitution.752 Deng et al. also showed that amino acids could be used as ligands in the copper-catalyzed borylation of primary and secondary alkyl bromides.753 Copper nanoparticles have also been shown to catalyze the borylation of primary and secondary alkyl halides with B2pin2 by both the Chung754 and the Xu755 groups. Alkyl chlorides are still very unreactive in many coppercatalyzed borylation reactions; however, one method has been previously reported for the borylation of primary alkyl chlorides by Gong, Jiang, and Fu using B2pin2, a rhodium catalyst and 2 equiv of NaOtBu, proving that these substrates under the right conditions undergo borylation successfully.756 The list of inexpensive metals available to catalyze this reaction has been growing with both zinc- and iron-catalyzed borylation reactions of alkyl halides being investigated. In 2014, Marder and co-workers reported the first zinc-catalyzed borylation of primary, secondary, and some tertiary alkyl halides.757 This was the second system that worked successfully to borylate tertiary alkyl halides, with only the nickel system discussed above having been reported previously.748,757 Following this, tertiary alkyl halides were also shown to undergo borylation by Cook et al.758 In this reaction, Fe(acac)3 and TMEDA were observed to facilitate the borylation of activated and unactivated alkyl halides using an excess of both B2pin2 and ethyl magnesium bromide. Furthermore, benzylic and allylic chlorides, tosylates, and mesylates also underwent

5.3. Alkyl Substitutions

In the presence of a zerovalent palladium catalyst, a phosphine ligand, and potassium acetate, Miyaura and co-workers discovered that allyl and benzyl halides could be borylated with B2pin2 (Scheme 95).30,31,741 Zerovalent palladium-based Scheme 95. Borylative Substitution of Alkyl Halides

catalysts continued to be investigated in the borylation of primary alkyl halides by Biscoe and co-workers,742 while Shi et al. recently published the direct borylation of benzyl alcohols in the absence of a base.743 In this case, it was proposed that the reaction went through a previously unobserved sp3 C−O bond activation facilitated by the palladium catalyst present.743 Molander and co-workers further demonstrated the utility of these reactions in the borylation of ethers744,745 and heterocycles746,747 (Scheme 96a). A similar reaction was published by Fu et al. with a nickel(II) bromide diiminopyridine catalytic system, which included tertiary alkyl halides (although not unactivated alkyl chlorides).748 The reactivity order in the reaction between primary, secondary, and tertiary alkyl halides was shown to be the opposite of that previously observed in nickel-catalyzed alkyl−alkyl cross-coupling.748,749 This interesting reaction observation was studied in more detail using DFT calculations by Lin and Marder et al.749 It was discovered that in the cross-coupling reaction, reductive elimination was rate limiting, as the steric hindrance from the tertiary alkyl halides increased the barrier in this particular step. However, the rate in the borylation reaction was determined by the atom transfer

Scheme 96. (a) Synthetic Route To Forming Potassium 2-(Trifluoroboratomethyl)-2,1-borazaraonaphthalenes and Subsequent Cross-Coupling Reaction with Aryl Chlorides; (b) Boryl Substitution of Alkyl Halides (right) and Borylative Cyclization of 6Bromo-hex-1-ene (left)

AN


Chemical Reviews

Review

borylation, affording moderate to good yields of the desired product.758,759 A few months later, Bedford and co-workers also reported a similar methodology using an iron(II)−chloridebased catalyst with phosphine ligands instead to borylate a range of alkyl halides with B2pin2 and exchanging the Grignard for tBuLi.233 The same group recently reported that cyclic sulfamidates act in a similar way to alkyl halides and are successfully borylated under slightly altered conditions to obtain (β- and γ-aminoalkyl)boronate esters, extending the substrate scope of the well-established copper-catalyzed borylation reactions.760

has proven to be a valuable and widely used synthetic methodology, the reaction can suffer from poor regiocontrol. To overcome this issue there has been considerable interest in the boryl substitutions of other functional groups on an aromatic ring using B2pin2. 5.5.1. Aryl Halides. Aryl halides are widely available and generally affordable reagents and thus were an excellent target for the borylation reaction. Borylations using basic organometallic reagents, such as organolithium and Grignard reagents, are well known; however, these reactions suffer from poor functional group tolerance. In rare cases, B2pin2 is used as the boron reagent in stoichiometric reactions with organolithium species (see Scheme 98 for example, section 5.4).769,770,782 The first report of the borylation of aryl halides using diboron(4) compounds was from Miyaura and co-workers in 1995 (Scheme 100)783 in which a palladium complex catalyzed the reaction in the presence of KOAc. The reported borylations of aryl iodides and bromides proved to have much more functional group tolerance than the synthesis of aryl boronates using organometallic reagents, with aldehyde, ketone, ester, imine, or nitrile functional groups being tolerated. This reaction has found widespread use in synthetic chemistry for the production of a vast array of aryl boronate esters. Experimental783 and computational784 studies of this reaction have suggested that the catalytic cycle begins with oxidative addition of the C−X bond at the zerovalent palladium center. Palladium(II) catalyst precursors can be used for the reaction; however, they are reduced in situ by the diboron and base additive to catalytically active zerovalent palladium complexes.785 Salt metathesis with KOAc generates an aryl palladium acetate species which subsequently undergoes transmetalation with B2pin2. Finally, the aryl−Bpin product is generated through reductive elimination (Scheme 101). The presence and nature of the base is vital to achieving high yields and selectivities. The use of stronger bases was found to promote Suzuki−Miyaura coupling of the aryl boronate ester product with the aryl halide starting material (a symmetrical Suzuki−Miyaura coupling reaction). As an interesting aside, Braun and co-workers also demonstrated that the oxidative addition products could be obtained from the initial stoichiometric reaction of SF5-functionalized aryl bromides and iodides with Pd(PiPr3)2, followed by the reaction of the corresponding palladium fluoride complex with B 2pin2, generating the desired aryl boronate ester.786 This borylation reaction has been used to convert polymerbound aryl halides to aryl boronates, which have been used for the preparation of polymer-bound biaryls that could subsequently be cleaved from the polymer.787,788 Lee and Kelly borylated aryl halides and then oxidized the product, replacing the boryl group with an hydroxyl group,789 whereupon the phenols were loaded onto a resin for solid-state synthesis. Giroux and co-workers reported a two-step, one-pot synthesis of biaryl species through the addition of an aromatic electrophile (aryl halide or pseudohalide) and sodium carbonate following completion of the borylation reaction

5.4. Alkenyl Substitutions

In the early 2000s, Miyaura reported the first borylations of alkenyl triflates and halides using palladium(II) chloride phosphine catalysts and a base additive (Scheme 97).761−764 Scheme 97. Borylation of Alkenyl Halides and Triflates

Later, the borylation of alkenyl triflates was used in the preparation of 4-aryl-tetrahydropyridines765 and tetrasubstituted alkenes.766 Xue et al. recently adapted this further to provide a more efficient route to forming 3,6-dihydro-2Hpyran-4-boronic acid pinacol esters in a one-pot synthesis.767 Alkenyl carbamates have been borylated using [NiCl2(PCy3)2] as a catalyst in the presence of K3PO4 and two additional equivalents of tricyclohexylphosphine.768 Lithium salts generated from terminal alkenyl halides and dihalides were borylated using a variety of diborons, producing gem-diboryl alkenes.769,770 The gem-diboryl alkenes could be stereoselectively coupled with aryl halides sequentially, producing tetrasubstituted alkenes (Scheme 98).771 Another report found that gem-diboryl alkenes reacted with 1-bromo-1lithioethene to form 2,3-bisboryl-1,3-dienes.772 The borylation of a vinyl bromide-containing heterocycle has been used in the preparation of a novel cyclic amino acid.773 Other nitrogen-containing heterocycles were also tolerant of the reaction conditions required for the borylation of alkenyl halides.774 Substitution of Bpin for a triflate group has been used in the construction of a polymer containing a novel extended π-conjugated system.775 Alkenyl iodides could be borylated with B2neop2 and subsequently reacted with Na123I to form 123I-substituted alkenes.776 In a similar fashion, vinyl sulfonates and phosphates of substituted tetrahydropyridines and other N-heterocyclic compounds were borylated and used in Suzuki−Miyaura coupling reactions (Scheme 99).777,778 5.5. Aromatic Substitutions

Given their utility in Suzuki−Miyaura cross-coupling reactions, the selective synthesis of aryl boronate esters is extremely important.779−781 While borylations of C−H bonds with B2pin2

Scheme 98. Borylative Route to Tetrasubstituted Alkenes via Borylation and Sequential Suzuki Cross-Coupling Reactions

AO


Chemical Reviews

Review

Scheme 99. Borylation and Suzuki−Miyaura Coupling of Substituted Tetrahydropyridines

et al. reported a study using a similar method, which facilitated the synthesis of several α,ω-pinacol boronates.811 The Suzuki− Miyaura reaction could subsequently be carried out without any purification steps required. In comparison with the analogous Stille coupling reaction, a one-pot borylation/Suzuki−Miyaura reaction resulting in the polymerization of bis-bromo thiophene-based monomers was found to be superior, producing higher quality, more homogeneous polymers.812 The borylation/Suzuki−Miyaura sequence outperformed alternative coupling methodologies in the synthesis of hippadine and pratosine, two naturally occurring biologically active molecules, although HBpin was found to be a more effective borylating agent than B2pin2 in this case (Scheme 103).813 Additionally, the one-pot borylation of aryl halides and subsequent symmetrical Suzuki−Miyaura cross-coupling has proven to be a useful synthetic technique.814 However, unintended symmetrical Suzuki−Miyaura reactions have occurred during the borylation of 8-bromoquinoline derivatives by [PdCl2(dppf)], even using KOAc, which is normally not a sufficiently strong base for the Suzuki−Miyaura coupling reaction.815 Zhang and co-workers successfully averted the symmetrical Suzuki−Miyaura reaction to allow the borylation of 8-bromo- and chloroquinolines by using Pd2(dba)3/nBuPAd2 (1:1.5 ratio) as the catalyst, DMAc as the solvent, and KOAc as the base additive.816 Under these conditions, the desired boronic acid was isolated following an aqueous workup or used in a one-pot Suzuki−Miyaura coupling.816 Firooznia and coworkers demonstrated that the chiral center in phenylalanine derivatives was preserved through one-pot borylation and Suzuki−Miyaura coupling reactions.817 Microwave heating could also be used to promote the borylation of aryl halides catalyzed by a palladium−NHC catalyst.818 While the borylation of ortho-substituted aryl halides was initially found to be much more difficult than with less hindered substrates, progress has been made by use of a Pd biphenyl dicyclohexyl phosphine catalyst system, which was shown to outperform palladium species with more labile ligands, including PPh3.819 Some bulky aryl iodides can undergo catalytic borylation using a [PdCl2(dppf)] catalyst system,820 while the Bedford palladacyclic precursor, in combination with

Scheme 100. Palladium-Catalyzed Borylation of Aryl Halides

Scheme 101. Proposed Mechanism for the PalladiumCatalyzed Borylation of Aryl Halides

(Scheme 102).790 The one-pot borylation/Suzuki−Miyaura reaction could also be used to generate polymers with Scheme 102. One-Pot Borylation/Suzuki−Miyaura Coupling Reaction without Added Catalyst

dihaloarenes.791 The borylation of aromatic C−X bonds has been exploited to prepare substituted porphyrin derivatives (including polymers).792,793 Indeed, a BINAP/BINOL polymer has also been prepared through borylation and subsequent Suzuki−Miyaura coupling.794 This ligand scaffold proved effective for tandem asymmetric catalysis. A related BINAPbased polymer was found to be similarly useful.795 Linking other ligands, such as bis-terpyridine, can be accomplished using the palladium-catalyzed borylation of aryl halides with B2pin2 or B2neop2.796−805 Likewise, arylpyridines have been borylated and subjected to Suzuki−Miyaura coupling.806 In related studies, thiopeptides807 and indazoles,808 dityrosine, and other polytyrosines809,810 were prepared using this borylation and Suzuki−Miyaura coupling methodology. More recently, Jin

Scheme 103. One-Pot Synthesis of Hippadine via Borylation/Suzuki−Miyaura Cross-Coupling/Lactamization

AP


Chemical Reviews

Review

Scheme 104. Synthesis of Biaryls by Borylation and Subsequent Suzuki−Miyaura Reactions, Catalyzed by a Palladacycle

was reported by Nechaev et al. for both the Miyaura borylation and the one-pot, two-step homocoupling of aryl halides.841 Palladium nanoparticles could be employed as the catalyst for borylation and one-pot borylation/Suzuki−Miyaura coupling.842,843 Palladium nanocrystals ligated by phosphines, generated in supercritical CO2, proved to be good catalysts for the borylation of aryl halides using 4-bromoanisole as a test substrate.844 Tricyclohexylphosphine and biaryl-dicyclohexylphosphine-ligated nanocrystals proved to be most active. Solidsupported palladium(II) bound to a silica surface through a phosphine ligand has likewise been used as a catalyst for the borylation of aryl halides.845−847 Although activity was high even with bulky chloroaryl substrates, attempts to reuse the catalyst were unsuccessful.845 Palladium(II) bound to a diphenyl phosphine-based silica support was found to be effective for the borylation of aryl halides in batch and flow reactor conditions.848−850 Tetrahydroxydiboron (B2(OH)4) is an alternate boron source for the borylation of aryl halides, as demonstrated by Molander and co-workers (Scheme 105), using a palladium(II)

biaryl phosphine ligands, gave a highly active catalyst system for the borylation of bulky aryl bromides.821 Additional palladacyclic catalyst precursors have been shown to be effective catalysts for the borylation of aryl halides and subsequent Suzuki−Miyaura reactions (Scheme 104).822−826 Notably, two reports also demonstrated that aryl bromides can be generated and subsequently borylated in situ with Nbromosuccinimide as the brominating agent.823,824 The use of [PdCl2(PCy3)2], instead of [PdCl2(dppf)], greatly accelerated borylation reactions of aryl bromides and triflates and, notably, allowed the use of aryl chlorides as substrates.68,827 Buchwald later reported that if XPhos was used as the ligand, the palladium-catalyzed borylation of aryl chlorides could be carried out at room temperature.828 This enhanced reactivity is attributed to the bulk of the biaryl phosphine ligand and the ability of KOAc to displace the palladium−arene interaction. Kwong and co-workers later reported a PPh 2-based phosphine ligand which, when combined with Pd2(dba)3, is a highly active and general catalyst system for the borylation of aryl chlorides and subsequent one-pot Suzuki−Miyaura coupling.829 Recently, Yu and co-workers tried to overcome some of the limitations in these systems, such as high catalyst loading or further addition of the catalyst to facilitate the subsequent coupling reaction. They established that some of these problems could be controlled by the use of 2-aryl indenyl phosphine ligands, which showed a very broad reaction scope in the palladium-catalyzed borylation/Suzuki cross-coupling reaction.830 Alternatively, monophosphine ligands have also been investigated to afford aryl boronates in high yields from the respective aryl chlorides.831 Furthermore, microwave radiation was useful in promoting the borylation of bulky aryl chlorides832 and accelerating reactions of aryl bromides.818,833 In 2003, Zhang and co-workers showed that palladium acetate, as the catalyst precursor for the borylation of aryl bromides, negated the requirement for phosphine ligands altogether by facilitating the formation of a palladium aryl acetate intermediate.834 A subsequent Suzuki−Miyaura crosscoupling was also carried out using this same catalyst system. Ionic liquids835 and polyethylene glycol836 have been used as alternative solvent systems for the borylation reaction. Palladium-catalyzed borylation of a wide range of aryl bromides could be done in water at room temperature using a surfactant to protect the catalyst.837,838 A biphasic system was employed successfully for the borylation and subsequent Suzuki−Miyaura coupling, showing enhanced reactivity for substrates containing electron-withdrawing groups, heterocycles, or bulky substituents.839 Different length chains of poly(ethylene)glycol have also been used to form novel NHCs, altering the behavior of the ligands, which were investigated in both borylation and Suzuki−Miyaura catalysis.840 Recently, a solvent-free system

Scheme 105. Borylation Using B2(OH)4 and Conversion to More Stable Trifluoroboronates

phenethylamine catalyst precursor.851,852 Importantly, the use of B2(OH)4 reduces the cost of the diboron reagent and means that pinacol will not need to be chemically removed and separated from the product following the reaction. Even aryl chlorides were subject to borylation using this protocol, and products were readily converted to aryl boronate esters or trifluoroborate salts. Interestingly, similar conditions were used as a part of a synthetic route to form MK-8876, which is a nonnucleoside inhibitor developed to help treat the Hepatitis C virus (HCV).853 One-pot borylation Suzuki−Miyaura coupling reactions could also be achieved using this palladium(II) catalyst.854 Further research into these systems was also conducted using a modified Pd catalyst and ethylene glycol as AQ


Chemical Reviews

Review

Scheme 106. (a) Generation and Borylation Reactions of B2(diol2) Species in Situ; (b) Borylation and Transesterification Reaction To Produce a Chiral Dienophile for Diels−Alder Reactions

metal options have increased in popularity over the past decade. A synergistic catalytic system utilizing palladium and copper catalysts was reported by Kiatisevi and co-workers.863 This system, which includes added phosphine ligand and excess base in the form of Cs2CO3, was found to be effective for the borylation of aryl iodides with B2pin2 in air at room temperature. The palladium catalyst is believed to activate the aryl carbon−iodide bond, while the copper catalyst serves as a transmetallating reagent. However, Marder and co-workers reported a pure copper-catalyzed borylation of aryl bromides and iodides with B2pin2 and B2neop2 at room temperature.231 A copper(I) salt (10 mol %), PnBu3 (13 mol %), and KOtBu (1.5 equiv) make up the catalytically active mixture. IPrCuOtBu also catalyzes the reactions but is slower than the PnBu3 system. A ligand-free variation of this method has also been published, which demonstrated the borylation of aryl bromides and iodides, as well as benzyl halides, though yields for these reactions were only moderate.864 Ishizuka and co-workers continued to investigate NHC ligands and showed that a bicyclic NHC−CuCl complex could successfully borylate a range of aryl halides but at slightly decreased yields compared to the seminal copper−phosphine system reported.865 Nickel has already been discussed briefly in the borylation of aryl halides with B2(OH)4 but has also been shown to catalyze the borylation of a large range of aryl chlorides using B2pin2, [NiCl2(PMe3)2], TMSOCH2CF3, and CsF.866 Furthermore, nickel catalysts have been utilized in several reactions by Darcel et al., forming aryl boronates in moderate yields.867,868 However, due to the toxic properties of nickel, alternative transition metals were investigated further. The groups of Takita and Uchiyama discovered the zinc(II)catalyzed borylation of aryl iodides and aryl bromides using pyrophoric Et2Zn as catalyst with B2pin2, B2cat2, and B2neop2 in the presence of excess NaOtBu, with THF as the solvent.599 Marder and Bose applied a similar method to their previously discussed zinc-catalyzed borylation of alkyl halides (section 5.3) in the borylation of aryl halides,757 thus providing a novel zinccatalyzed reaction with B2pin2 under much milder conditions.869 During their investigations, an interesting subset of reactions was discovered when the ligand was changed to 4,4′di-tert-butyl-2,2′-bipyridine (dtbpy). This ligand facilitated the borylation of not only the C−X group but also the adjacent C−

the additive. The presence of the ethylene glycol led to a reduction in the amount of diboron required as well as faster reaction times and a larger substrate scope.855 A catalytic system comprising of [NiCl2(dppp)] (dppp = 1,3-bis(diphenylphosphino)propane) and 2 equiv of PPh3 proved to be more tolerant of carbonyl groups and functioned at lower temperatures than the corresponding palladium systems.856 An alternative nickel-based catalyst, [NiCl(o-tolyl)(TMEDA)], was also investigated under similar conditions in the reaction between aryl bromides and B2(OH)4, affording a moderate to good yield of the desired aryl boronate ester, thus indicating that nickel catalysts are a good alternative to the previously used palladium complexes.857 The Molander group also demonstrated the use of tetrakis(dimethylamino)diboron (B2(NMe2)4) as the borylating agent for aryl chlorides and bromides.858 Additionally, B2(NMe2)4 was also used as the starting diboron(4) compound in the borylation of aryl bromides by an in situ generated B2(diol)2 (Scheme 106a).859 Complete conversion to the B2(diol)2 from B2(NMe2)4 and 2 equiv of diol was observed in solution, and the reactivity of the borylated products in a subsequent (one-pot) Suzuki−Miyaura reaction differed, based on the nature of the diol used. An elegant synthesis of a 2boronoacrylanilides from Kennedy and Hall utilized the borylation of an aryl bromide with B2neop2.860 The aryl boronate ester could undergo transesterification with chiral diols. Several subsequent steps produced monosubstituted terminal alkenes (Scheme 106b), which showed low degrees of diastereoselectivity as dienophiles in ensuing Diels−Alder reactions. The borylation of aryl iodides with B2neop2 was reported to be a useful step in the preparation of isotopically enriched aryl iodides861 by subsequently reacting the aryl boronate ester with Na123I to produce the 123I-enriched aryl iodide. Nonsymmetrical diboron(4) compounds have also been investigated in the borylation of aryl halides. Li et al. published the use of BpinBdan in the borylation of both aryl bromides and chlorides in the presence of a palladium catalyst. The formation of the ArBdan product illustrated the potential of the Bdan group to form a range of masked boronic acids.862 Palladium catalysts have facilitated a myriad of borylation reactions; however, alternative more affordable and abundant AR


Chemical Reviews

Review

4-boryltetrafluoropyridine is obtained.877 Subsequently, Zhang et al. reported that N-heterocyclic-substituted polyfluoroarenes could also undergo ortho-selective C−F bond borylation with B2pin2 using [Rh(COD)2]BF4. Mechanistic studies suggested that a rhodium(III) hydride complex, [(H)RhIIILn(Bpin)], was a key intermediate in the catalytic cycle.878 Several research groups have also exchanged the rhodium catalysts for nickel species. Martin’s and Hosoya’s groups simultaneously reported the borylation of monofluoroarenes (Scheme 108b). Martin et al. used a combination of Ni(COD)2 and PCy3 with B2neop2 to borylate aryl fluorides (Scheme 108b, right), while Hosoya and co-workers used the same catalyst but with the additional help of CuI to borylate monofluoroarenes with B2pin2 (Scheme 108b, left).879,880 As an interesting aside, several reports have shown that B2pin2 can also be used as a cocatalyst in copper-catalyzed fluorination/fluoroalkylation reactions. Szabó et al. reported that B2pin2 may accelerate the C−H trifluoromethylation of quinones,881 while a similar effect was observed by Zhang and co-workers in the aminofluorination of styrenes.882 Furthermore, Ding, Wang, and co-workers observed that stoichiometric amounts of B2pin2 were required to facilitate the transition-metal-catalyzed C−F activation in the iridiumcatalyzed synthesis of symmetrical diaryl ethers from fluorarenes.883 5.5.2. Aryl C−O Electrophiles. Different C−O bondcontaining aryl electrophiles, such as aryl triflates, have been successfully used as an alternative to aryl halides in borylation reactions. The first such report came from Miyaura and coworkers884 and conditions employed varied slightly from those used initially in the halide substitution reaction, as dioxane was used as a solvent and extra dppf ligand was required to prevent catalyst deactivation and decomposition to palladium black.68 Two-step, one-pot reactions have been reported, which incorporate an unsymmetrical790,884 or symmetrical814 Suzuki−Miyaura cross-coupling reaction after the borylation step. Symmetrical Suzuki−Miyaura coupling of naphthyl triflates has been used as part of an approach to the synthesis of crisamicin A, a compound which has previously demonstrated antiviral properties.885−887 The use of B2neop2 as the borylating agent, instead of B2pin2, was found to assist the borylation of orthosubstituted aryl triflates.888 A 2-phenyl-4-oxazolylboronate could be prepared by borylation of the corresponding triflate.889 Aryl triflates have been reported to be converted to aryl iodides through borylation with B2neop2 and subsequent reaction with NaI and chloramine-T.890 As an extension to this chemistry, aryl tosylates and mesylates can also be borylated. These reagents are particularly useful in that they allowed for the borylation of a large family of alcohol substrates through an initial sulfonation step. Aryl mesylates and tosylates also tend to be significantly more stable and easier to isolate than their triflate counterparts. Kwong and co-workers first demonstrated that aryl mesylates and tosylates can be borylated with B2pin2, Pd(OAc)2, a phosphine ligand, and KOAc (Scheme 109).891 Other diboron reagents were used in this type of reaction; however, reactions with B2pin2 produced the highest yields. One-pot Suzuki−Miyaura coupling was also possible with this system. A 2011 report from Shi and co-workers documented the ability of bis(tricyclohexylphosphine)nickel(II) chloride to catalyze the borylation of aryl carboxylates with B2neop2.768 Stoichiometric amounts of NaOtBu or K3PO4 and two additional equivalents of tricyclohexylphosphine were required

H group to form a range of 1,2-bis(Bpin) benzenes (Scheme 107).870,871 Scheme 107. Zinc-Catalyzed Borylation of Aryl Halides To Afford 1,2-Bis(Bpin) Benzenes

Interestingly, several reports have recently been published on metal-free borylations of aryl electrophiles. Initially, Zhang and co-workers published results on the borylation of aryl iodides but not aryl bromides or chlorides with B2pin2, mediated by Cs2CO3 in methanol.872 More recently, Muñiz et al. established that diaryliodonium salts could also be combined with B2pin2 in methanol to provide a metal-free borylation route to aryl boronate esters in moderate to good yield.873 Furthermore, Li reported an efficient continuous flow photolytic borylation of aryl iodides and bromides in aqueous solution.874 Several different diboron sources were examined including B2pin2, B2neop2, BpinBdan, and B2(OH)4, with the product from the latter diboron source converted directly with KHF2 to generate the potassium aryl trifluoroborate.874 Subsequently, Larionov et al. showed that the photoinduced borylation of haloarenes, including electron-rich fluoroarenes, with B2(OH)4 could be conducted under metal- and additive-free conditions.875 Under the same conditions, quaternary arylammonium salts were also shown to undergo borylation.875 Finally, Marder, Perutz, and co-workers published a rare example of stoichiometric C−F borylation of pentafluoropyridine using a rhodium(I) complex. The reaction occurred at the 2- and 4-positions, and full conversion required 2 equiv of B2cat2 to produce the borylated pyridine and a triborylrhodium complex. Braun, Macgregor, and co-workers were able to develop a closely related catalytic reaction pathway for C−F bond activation using a rhodium(I) boryl catalyst (Scheme 108a),876 while further investigations reported several years later showed that the regioselectivity of the borylation reaction of pentafluoropyridine is governed by the choice between B2pin2 and HBpin. When B2pin2 is used, the pyridine is borylated at the 2-position, while in the presence of HBpin, the Scheme 108. (a) Borylation of an Aromatic C−F Bond; (b) Two Synthetic Pathways to Monosubstituted Aryl Boronate Esters

AS


Chemical Reviews

Review

Scheme 109. Palladium-Catalyzed Borylation of Aryl Mesylates and Tosylates

metric reactions of several isolated anionic Lewis base adducts with different substituted aryl diazonium salts.232 The adducts reacted successfully with the pure aryl diazonium salts, showing that the in situ-formed anionic adducts could play a vital role as the nucleophilic boryl source in the reaction.232 Furthermore, several research groups attempted to improve the reaction conditions by one group observing that the borylation could be conducted in water at room temperature with B2(OH)4,908 while another group showed that the reaction with either bisboronic acid or B2pin2 could function in pure methanol.909 As an interesting aside, Toste and co-workers have recently shown that an aryl diazonium salt can also be used, alongside αolefins and B2pin2, in enantioselective 1,1-arylborylation of alkenes to synthesize chiral benzylic boronate esters.910 In 2014, Tobisu, Nakamura, and Chatani established a synthetic pathway to aryl boronate esters from N-aryl amides and B2neop2 (Scheme 111a).911 The reactions required a

for optimal reactivity. Aryl carbamates were found to be especially active, partly due to their stability to hydrolysis.768 Additionally, aryl 2-pyridyl ethers892 and aryl pivalates893 were successfully borylated by diboron(4) reagents using a rhodium catalyst. Finally, the simplest reagent in the phenol series was also established as a good alternative to aryl halides. In 2014, Martin and co-workers observed that aryl ethers could undergo ipsoborylation in the presence of a nickel catalyst, Ni(COD)2, and a phosphine ligand, PCy3,894 while a similar system was used by Chatani et al. to form a one-pot synthesis in a range of symmetrical biaryls.895 In these reactions, the phosphine ligand has been exchanged for an NHC, and it is noteworthy that no biaryl homocoupling product was observed under identical conditions to those used by Martin and co-workers.895 5.5.3. Aryl C−N Bonds. Perhaps not surprisingly, aryl diazonium tetrafluoroborates serve as electrophiles for the palladium(II)-catalyzed borylation reaction.896 The reaction was found to proceed in the absence of a base at 60 °C,896 though addition of an NHC ligand allowed the reaction to proceed efficiently at room temperature.897 The reaction was later found to work in water at room temperature with CuBr as the catalyst and is tolerant of a wide variety of functional groups.898 More recently, aryl diazonium salts have been used in a transition-metal-free borylation reaction, mediated by PPh3, and conducted under mild conditions.899 The availability and relatively low cost of aryl amines compared to aryl halides gave an alternative substrate to be used in aryl borylation reactions.900 Wang and co-workers reported one-pot, two-step transformations of aryl amines to aryl boronates, which proceeded through the generation of the diazonium salt in a Sandmeyer-like fashion, followed by metalfree borylation.900,901 The reaction was optimized and shown to be quite general, while the proposed mechanism is believed to involve a single electron transfer step from a boryl anion formed in situ from the reaction of KOAc with B2pin2 (Scheme 110).902,903 The same group continued to improve the

Scheme 111. Nickel-Catalyzed Borylation of N-Aryl Amides (a) and Aryl Ammonium Salts (b) with Diboron(4) Compounds

relatively high loading of Ni(COD)2 (10 mol %), imidazolium salt (10 mol %), and NaOtBu (20 mol %) and heating at 160 °C in toluene for 20 h.911 However, borylation of tertiary and benzylic amines remained unexplored until an investigation by Itami et al., in which they established that aryl ammonium salts could undergo borylation in the presence of Ni(COD)2 and trin-butylphopshine in dioxane (Scheme 111b).912 Furthemore, the reaction scope was expanded to incorporate benzylic ammonium salts using a slightly different nickel catalyst, Ni(NO3)2·6H2O.912 Subsequently, a similar set of reactions was reported by Shi and co-workers that could be used to borylate the same sp2 and sp3 C−N bonds.913 Indoline and 1,2,3,4tetrahydroquinoline were also investigated under the same conditions and shown to undergo ring opening via borylative cleavage of the C−N bond.913 Additionally, enantioenriched benzylic boronates were briefly mentioned in the same publication but extended upon in greater detail by a following report from Watson and co-workers.914 They demonstrated that the catalytic combination of Ni(COD)2 and PPh3 could facilitate the borylation of secondary benzylic ammonium salts to generate highly enantioselective benzylic boronates. 5.5.4. Aryl Nitriles. Chatani, Tobisu, and co-workers pioneered the development of aryl nitrile borylation with

Scheme 110. Metal-Free Borylation of Aryl Amines

synthetic route by showing that aryl borylation can be conducted on a larger scale and used this method to generate aromatics substituted with both stannyl and boryl functionalities, allowing for one-pot sequential Stille and Suzuki− Miyaura coupling reactions.904−906 Furthermore, diazonium salts were also generated in situ during the borylation of aryltriazene to form the respective aryl boronate ester. Under identical conditions, the aryl triazene was replaced by the aryl diazonium salt to obtain the same product as previously synthesized.907 Additionally, Yamane and Zhu proposed the formation of an [B2pin2F]− adduct, which was necessary to facilitate the reaction.907 These findings were analyzed further when Marder et al. examined the stoichioAT


Chemical Reviews

Review

B2neop2.915,916 In the presence of a rhodium catalyst, 2 equiv of B2neop2, and 1 equiv of base, aryl nitriles bearing a wide variety of functional groups can be selectively borylated (Scheme 112).

Biographies Emily Neeve was born in Canterbury, United Kingdom. She received her MSci (Hons) degree in Chemistry from the University of Bristol, U.K., in 2009 and her Ph.D. degree at the same university in 2013 with Professor Robin B. Bedford, working on iron-catalyzed cross-coupling reactions. During her Ph.D. studies she also spent 1 month at the École Normale Supérieure in Paris, France, with Professor Anny Jutand. Since 2013, she has been a postdoctoral fellow in Professor Todd Marder’s group at the Julius-Maximilians-Universität Würzburg, Germany, examining the chemistry of anionic diboron adducts and their role in borylation reactions.

Scheme 112. Rhodium-Catalyzed Borylation of Aryl Nitriles

Steve Geier is a native of Sackville, New Brunswick. He completed his B.Sc. degee at Mount Allison University and went on to pursue his Ph.D. degree at the University of Windsor under the supervision of Dr. Douglas W. Stephan. His Ph.D. work focused on “Frustrated Lewis Pair” chemistry. He accompanied Dr. Stephan in his move to the University of Toronto. Following completion of his Ph.D. degree in 2010, he spent 2 years as an NSERC Postdoctoral Fellow in the lab of Dr. Jeffrey R. Long at the University of California, Berkeley. He then returned to Sackville to help Stephen A. Westcott and has been a Research Associate of Dr. Stephen A. Westcott’s group at Mount Allison University since January 2013. His research interests include all things boron.

The proposed mechanism involves transmetalation of B2neop2 with the rhodium complex, followed by nitrile insertion into the rhodium−boron bond, E/Z isomerization of the imine, and then β-arene elimination. The mechanism of this reaction was recently investigated in greater detail by Liu et al.917 5.6. Diagram Summarizing Section 5

Ibraheem Mkhalid was born in Jeddah, Saudi Arabia, in 1976. He received his B.Sc. degree from King Abdul Aziz University (1999) and his Ph.D. degree from Durham University (2006) for work on transition-metal-catalyzed borylation of C−H bonds carried out under the supervision of Professor Todd B. Marder. In 2006, he returned to King Abdul Aziz University as Assistant Professor in the Chemistry Department. Now, he is an Associate Professor at the same department. Steve Westcott was born in the 1960s somewhere around Tecumseh and received his Ph.D. degree from the University of Waterloo under the joint supervision of Drs. Todd B. Marder (now at Universität Würzburg) and R. Tom Baker (now at the University of Ottawa) working on metal-catalyzed hydroborations. He was an NSERC PDF, where he spent 1 year at Emory University in Atlanta with Dr. Lanny Liebeskind and more than 1 year working with Dr. Maurice Brookhart at the University of North Carolina at Chapel Hill, NC. He has been at Mount Allison University since August 1995 and is currently a Canada Research Chair in Boron Chemistry. His research interests include catalysis and the synthesis and development of biologically active boron and transition-metal compounds.

6. CONCLUSION While just synthetic inorganic curiosities for ca. 70 years, since the mid-1990s the profound impact of diboron(4) reagents on modern synthetic chemistry is undeniable. Further adding to their synthetic utility of these reagents are the straightforward methods to prepare these remarkable synthons, which are now commercially available in bulk quantities. With the development of the Suzuki−Miyaura reaction, other C−C and C− element coupling reactions, as well as numerous functional group transformations, organoboronates have become extremely important synthetic building blocks. In addition to metal-catalyzed diborations, β-borylations, and C−H and C−X borylations, important recent developments include metal-free catalytic borylations and new catalyst systems which can function in water under an atmosphere of air. These userfriendly advances as well as the continuing development of entirely new applications will certainly help to ensure an important place for diboron(4) compounds in synthesis for many years to come.

Todd Marder received his B.Sc. degree in Chemistry from M.I.T. (1976) and his Ph.D. degree from the University of California at Los Angeles (1981), where he was a University of California Regents Intern Fellow. Following postdoctoral research at the University of Bristol in England, he spent 2 years as a Visiting Research Scientist at DuPont Central Research in Wilmington. He joined the faculty at the University of Waterloo, Canada, in 1985 and in 1995 was awarded the Rutherford Memorial Medal for Chemistry of the Royal Society of Canada. He moved to the University of Durham in England in 1997 to take the Chair in Inorganic Chemistry previously held by Ken Wade. In 2008, he received the RSC Award in Main Group Element Chemistry. In 2010, he was awarded a JSPS Invitation Fellowship, a Humboldt Research Award, and a Royal Society Wolfson Research Merit Award. In 2012, he accepted a Chair in Inorganic Chemistry at the University of Würzburg, Germany, a major center for boron and organometallic chemistry. In 2015, he was elected to the Bavarian Academy of Sciences and was the recipient of the RSC Award in Organometallic Chemistry. He holds or has held Visiting/Honorary/

AUTHOR INFORMATION Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest. AU


Chemical Reviews

Review

(21) Simpson, P. G.; Folting, K.; Lipscomb, W. N. The Molecular Structure of i-B18H22. J. Am. Chem. Soc. 1963, 85, 1879−1880. (22) Lewin, R.; Simpson, P. G.; Lipscomb, W. N. Molecular and Crystal Structure of C2H5NH2B8H11NHC2H5. J. Chem. Phys. 1963, 39, 1532−1537. (23) Corcoran, E. W.; Sneddon, L. G. Transition-Metal-Promoted Reactions of Boron Hydrides. 4. A One-Step Synthesis of the Coupled Cage Borane 1,2′-[B5H8]2. Inorg. Chem. 1983, 22, 182. (24) Soderquist, J. A.; Brown, H. C. Simple, Remarkably Efficient Route to High Purity, Crystalline 9-Borabicyclo[3.3.1]nonane (9BBN) Dimer. J. Org. Chem. 1981, 46, 4599−4600. (25) The 2010 Nobel Prize was shared equally with Richard F. Heck and Ei-ichi Negishi. (26) Welch, C. N.; Shore, S. G.; Boron Heterocycles, V. Preparation and Characterization of Selected Heteronuclear Diboron Ring Systems. Inorg. Chem. 1968, 7, 225−230. (27) Biffar, W.; Nöth, H.; Pommerening, H.; Wrackmeyer, B. NMRStudies of Boron-Compounds Kernresonanzspektroskopische Untersuchungen an Bor-Verbindungen, XVII. 17O-NMR-Studien an Organyloxyboranen, Organyloxydiboranen(4), Dioxaborolanen und Boroxinen. Chem. Ber. 1980, 113, 333−341. (28) Ishiyama, T.; Murata, M.; Ahiko, T.-A.; Miyaura, N. Bis(pinacolato)diboron. Org. Synth. 2000, 77, 176−185. (29) Nguyen, P.; Lesley, G.; Taylor, N. J.; Marder, T. B.; Pickett, N. L.; Clegg, W.; Elsegood, M. R. J.; Norman, N. C. Oxidative Addition of B-B Bonds by Rhodium(I) Phosphine Complexes: Molecular Structures of B2cat2 (cat = 1,2-O2C6H4) and Its 4-But and 3,5-But2 Analogs. Inorg. Chem. 1994, 33, 4623−4624. (30) Ishiyama, T.; Miyaura, N. Synthesis of Organoboron Compounds via the Transition Metal-Catalyzed Addition and Coupling Reaction of (Alkoxo)diborons. Yuki Gosei Kagaku Kyokaishi 1999, 57, 503−511. (31) Ishiyama, T.; Miyaura, N. Chemistry of Group 13 ElementTransition Metal Linkage - the Platinum- and Palladium-Catalyzed reactions of (Alkoxo)diborons. J. Organomet. Chem. 2000, 611, 392− 402. (32) Ramírez, J.; Lillo, V.; Segarra, A. M.; Fernández, E. Catalytic Asymmetric Boron−Boron Addition to Unsaturated Molecules. C. R. Chim. 2007, 10, 138−151. (33) Irvine, G. J.; Lesley, M. J. G.; Marder, T. B.; Norman, N. C.; Rice, C. R.; Robins, E. G.; Roper, W. R.; Whittell, G. R.; Wright, L. J. Transition Metal−Boryl Compounds: Synthesis, Reactivity, and Structure. Chem. Rev. 1998, 98, 2685−2722. (34) Miyaura, N. Metal-Catalyzed Reactions of Organoboronic Acids and Esters. Bull. Chem. Soc. Jpn. 2008, 81, 1535−1553. (35) Ali, H. A.; Dembitsky, V. M.; Srebnik, M. Recent Developments in Bisdiborane Chemistry: B-C-B, B-C-C-B, B-CC-B, and B-C≡C-B Compounds and Their Biological Applications. Stud. Inorg. Chem. 2005, 22, 59−117. (36) Ali, H. A.; Dembitsky, V. M.; Srebnik, M. Chemistry of the Diboron Compounds. Stud. Inorg. Chem. 2005, 22, 1−57. (37) Dembitsky, V. M.; Ali, H. A.; Srebnik, M. Recent Developments in Bisdiborane Chemistry: B-C-B, B-C-C-B, B-CC-B and BC CB Compounds. Appl. Organomet. Chem. 2003, 17, 327−345. (38) Shimizu, M.; Hiyama, T. Polyborylated Reagents for Modern Organic Synthesis. Proc. Jpn. Acad., Ser. B 2008, 84, 75−85. (39) Beletskaya, I.; Moberg, C. Element−Element Additions to Unsaturated Carbon−Carbon Bonds Catalyzed by Transition Metal Complexes. Chem. Rev. 2006, 106, 2320−2354. (40) Burks, H. E.; Morken, J. P. Catalytic Enantioselective Diboration, Disilation and Silaboration: New Opportunities for Asymmetric Synthesis. Chem. Commun. 2007, 4717−4725. (41) Onozawa, S.-Y.; Tanaka, M. Activation of Boron-Heteroatom Bonds by Transition Metals and Its Application to Organic Synthesis. Yuki Gosei Kagaku Kyokaishi 2002, 60, 826−836. (42) Ishiyama, T.; Miyaura, N. Metal-Catalyzed Reactions of Diborons for Synthesis of Organoboron Compounds. Chem. Rec. 2004, 3, 271−280.

Distinguished Professorships in the United Kingdom, France, Hong Kong, mainland China, and Japan and was the 2014 Craig Lecturer at ANU. He has served on the editorial boards of Organometallics, Inorganic Chemistry, The Journal of Organometallic Chemistry, Polyhedron, Inorganica Chimica Acta, Applied Organometallic Chemistry, The Canadian Journal of Chemistry, Crystal Engineering, etc. His diverse research interests include synthesis, structure, bonding, and reactivity of organometallic and metal−boron compounds, homogeneous catalysis, small molecule triggers of stem cell differentiation, luminescence, nonlinear optics, liquid crystals, and crystal engineering.

ACKNOWLEDGMENTS T.B.M. thanks the DFG and the University of Würzburg for support. S.A.W. thanks Chris Vogels for helpful discussions and NSERC of Canada for support. REFERENCES (1) Stock, A.; Brandt, A.; Fischer, H. Der Zink-Lichtbogen als Reduktionsmittel. Ber. Dtsch. Chem. Ges. B 1925, 58, 643−657. (2) Yang, W.; Gao, X.; Wang, B. Boronic Acid Compounds as Potential Pharmaceutical Agents. Med. Res. Rev. 2003, 23, 346−368. (3) Lipscomb, W. N. The Boranes and Their Relatives. Science 1977, 196, 1047−1055. (4) Negishi, E. I.; Racherla, U. S. A Tribute to Herbert C. Brown. Heteroat. Chem. 1992, 3, 201−208. (5) Suzuki, A. Cross-Coupling Reactions of Organoboranes: An Easy Way To Construct C-C Bonds (Nobel Lecture). Angew. Chem., Int. Ed. 2011, 50, 6722−6737. (6) Dilthey, W. Uber die Konstitution des Wassers. Angew. Chem. 1921, 34, 596. (7) Price, W. The Structure of Diborane. J. Chem. Phys. 1947, 15, 614. (8) Longuet-Higgins, H.; Roberts, M. d. V. The Electronic Structure of an Icosahedron of Boron Atoms. Proc. R. Soc. London, Ser. A 1955, 230, 110−119. (9) Eberhardt, W.; Crawford, B.; Lipscomb, W. The Valence Structure of the Boron Hydrides. J. Chem. Phys. 1954, 22, 989−1001. (10) Hoffmann, R.; Lipscomb, W. N. Intramolecular Isomerization and Transformations in Carboranes and Substituted Polyhedral Molecules. Inorg. Chem. 1963, 2, 231−232. (11) Grimes, R.; Wang, F. E.; Lewin, R.; Lipscomb, W. N. A New Type of Boron Hydride, B10H16. Proc. Natl. Acad. Sci. U. S. A. 1961, 47, 996−999. (12) Rušcǐ c, B.; Schwarz, M.; Berkowitz, J. Molecular Structure and Thermal Stability of B2H4 and B2H4+ Species. J. Chem. Phys. 1989, 91, 4576−4581. (13) Herndon, W. C.; Ellzey, M. L. Resonance Energies and ΔH (Atomization) for Boron Hydrides. Inorg. Nucl. Chem. Lett. 1980, 16, 361−366. (14) Dewar, M. J.; McKee, M. L. Ground States of Molecules. 47. MNDO Studies of Boron Hydrides and Boron Hydride Anions. Inorg. Chem. 1978, 17, 1569−1581. (15) Hall, L. H.; Koski, W. S. On the Nature of Some Higher Boron Hydrides Produced in Radiation-Induced Reactions in Penta- and Decaborane. J. Am. Chem. Soc. 1962, 84, 4205−4207. (16) McLaughlin, E.; Hall, L. H.; Rozett, R. W. Monoisotopic Mass Spectra of Some Boranes and Borane Derivatives. J. Phys. Chem. 1973, 77, 2984−2988. (17) Pauling, L. The Composition of the Boranes. J. Inorg. Nucl. Chem. 1970, 32, 3745−3749. (18) Gunn, S. R.; Kindsvater, J. H. The Heats of Decomposition of Some More Boron Hydrides. J. Phys. Chem. 1966, 70, 1114−1119. (19) Moore, E. B. Molecular Orbitals in B5H9 and B10H16. J. Am. Chem. Soc. 1963, 85, 676−679. (20) Grimes, R. N.; Lipscomb, W. N. Decaborane (16): Its Rearrangement to Decaborane (14) and Cleavage. Proc. Natl. Acad. Sci. U. S. A. 1962, 48, 496−499. AV


Chemical Reviews

Review

(43) Dang, L.; Lin, Z.; Marder, T. B. Boryl Ligands and Their Roles in Metal-Catalysed Borylation Reactions. Chem. Commun. 2009, 3987−3995. (44) Jeganmohan, M.; Cheng, C.-H. Transition Metal-Catalyzed Three-Component Coupling of Allenes and the Related Allylation Reactions. Chem. Commun. 2008, 3101−3117. (45) Lillo, V.; Bonet, A.; Fernández, E. Asymmetric Induction on βBoration of α,β-Unsaturated Compounds: an Inexpensive Approach. Dalton Trans. 2009, 2899−2908. (46) Ramírez, J.; Lillo, V.; Segarra, A. M.; Fernández, E. Catalytic Tandem Organic Sequences Through Selective Boron Addition Chemistry. Curr. Org. Chem. 2008, 12, 405−423. (47) Broene, R. D.; Baker, R. T. Encyclopedia of Catalysis; WileyInterscience: New York, 2002. (48) Pubill-Ulldemolins, C.; Bonet, A.; Bo, C.; Gulyás, H.; Fernández, E. A New Context for Palladium Mediated B-Addition Reaction: an Open Door to Consecutive Functionalization. Org. Biomol. Chem. 2010, 8, 2667−2682. (49) Braunschweig, H.; Colling, M. Transition Metal Complexes of Boron - Synthesis, Structure and Reactivity. Coord. Chem. Rev. 2001, 223, 1−51. (50) Braunschweig, H.; Kupfer, T. [n]Borametalloarenophanes (n = 1, 2): Strained Systems with Uncommon Reactivity Patterns. Eur. J. Inorg. Chem. 2012, 1319−1332. (51) Hartwig, J. F. Regioselectivity of the Borylation of Alkanes and Arenes. Chem. Soc. Rev. 2011, 40, 1992−2002. (52) Marder, T. B.; Norman, N. C. Transition Metal Catalyzed Diboration. Top. Catal. 1998, 5, 63−73. (53) Takaya, J.; Iwasawa, N. Catalytic, Direct Synthesis of Bis(boronate) Compounds. ACS Catal. 2012, 2, 1993−2006. (54) Liu, X. Bis(pinacolato)diboron. Synlett 2003, 2442−2443. (55) Pilarski, L. T.; Szabó, K. J. Palladium-Catalyzed Direct Synthesis of Organoboronic Acids. Angew. Chem., Int. Ed. 2011, 50, 8230−8232. (56) Beletskaya, I.; Moberg, C. Element-Element Addition to Alkynes Catalyzed by the Group 10 Metals. Chem. Rev. 1999, 99, 3435−3461. (57) Mkhalid, I. A. I.; Barnard, J. H.; Marder, T. B.; Murphy, J. M.; Hartwig, J. F. C−H Activation for the Construction of C−B Bonds. Chem. Rev. 2010, 110, 890−931. (58) Ros, A.; Fernández, R.; Lassaletta, J. M. Functional Group Directed C-H Borylation. Chem. Soc. Rev. 2014, 43, 3229−3243. (59) Hartwig, J. F. Borylation and Silylation of C-H Bonds: A Platform for Diverse C-H Bond Functionalizations. Acc. Chem. Res. 2012, 45, 864−873. (60) Boebel, T. A.; Hartwig, J. F. Iridium-Catalyzed Preparation of Silylboranes by Silane Borylation and Their Use in the Catalytic Borylation of Arenes. Organometallics 2008, 27, 6013−6019. (61) Holliday, A.; Massey, A. G. Boron Subhalides and Related Compounds with Boron-Boron Bonds. Chem. Rev. 1962, 62, 303−318. (62) Holliday, A. K.; Massey, A. G. The Preparation of Diboron Tetrachloride. J. Am. Chem. Soc. 1958, 80, 4744−4745. (63) Wartik, T.; Moore, R.; Schlesinger, H. I. Derivatives of Diborine. J. Am. Chem. Soc. 1949, 71, 3265−3266. (64) Urry, G.; Wartik, T.; Moore, R. E.; Schlesinger, H. I. The Preparation and Some of the Properties of Diboron Tetrachloride, B2Cl4. J. Am. Chem. Soc. 1954, 76, 5293−5298. (65) Massey, A. G.; Urch, D. S.; Holliday, A. K. Preparation of Diboron Tetrachloride and Other Boron Sub-Chlorides. J. Inorg. Nucl. Chem. 1966, 28, 365−370. (66) Timms, P. L. Chemistry of Transition-Metal Vapours. Part II. Preparation of Diboron Tetrachloride from Copper Vapor and Boron Trichloride. J. Chem. Soc., Dalton Trans. 1972, 830−832. (67) Timms, P. L. Chemical Reactions of Boron Atoms. Chem. Commun. 1968, 258−259. (68) Dembitsky, V. M.; Ali, H. A.; Srebnik, M. Recent Chemistry of the Diboron Compounds. Advances in Organometallic Chemistry; Academic Press: Cambridge, 2004; pp 193−250. (69) Timms, P. L. Reaction of Copper Atoms with Boron-Chlorine Compounds. Chem. Commun. 1968, 1525a.

(70) Westcott, S. A.; Fernández, E. Chapter Two - Singular Metal Activation of Diboron Compounds. Advances in Organometallic Chemistry; Academic Press: Cambridge, 2015; pp 39−89. (71) Frazer, J. W.; Holzmann, R. T. Microwave Excitation as a Synthetic Tool: The Preparation of Diboron Tetrachloride. J. Am. Chem. Soc. 1958, 80, 2907−2908. (72) McCloskey, A. L.; Brotherton, R. J.; Boone, J. L. The Preparation of Boron Monoxide and its Conversion to Diboron Tetrachloride. J. Am. Chem. Soc. 1961, 83, 4750−4754. (73) Nöth, H.; Pommerening, H. Beiträge zur Chemie des Bors, Eine Einfache Synthese von Dibortetrabromid. Chem. Ber. 1981, 114, 398− 399. (74) Schumb, W. C.; Gamble, E. L.; Banus, M. D. Lower Iodides of Boron. J. Am. Chem. Soc. 1949, 71, 3225−3229. (75) Morrison, J. A. Chemistry of the Polyhedral Boron Halides and the Diboron Tetrahalides. Chem. Rev. 1991, 91, 35−48. (76) Finch, A.; Schlesinger, H. I. Diboron Tetrafluoride. J. Am. Chem. Soc. 1958, 80, 3573−3574. (77) Timms, P. L. Boron-Fluorine Chemistry. I. Boron Monofluoride and Some Derivatives. J. Am. Chem. Soc. 1967, 89, 1629−1632. (78) Timms, P. L. Chemistry of Boron and Silicon Subhalides. Acc. Chem. Res. 1973, 6, 118−123. (79) Lynaugh, N.; Lloyd, D.; Guest, M.; Hall, M.; Hillier, I. Photoelectron Studies of Boron Compounds. Part 4. - Experimental and Theoretical Studies of Diboron Tetrachloride and Diboron Tetrafluoride. J. Chem. Soc., Faraday Trans. 2 1972, 68, 2192−2199. (80) Urry, G.; Kerrigan, J.; Parsons, T. D.; Schlesinger, H. Diboron Tetrachloride, B2Cl4, as a Reagent for the Synthesis of Organo-boron Compounds. I. The Reaction of Diboron Tetrachloride with Ethylene. J. Am. Chem. Soc. 1954, 76, 5299−5301. (81) Urry, G.; Garrett, A. G.; Schlesinger, H. The Chemistry of the Boron Subhalides. I. Some Properties of Tetraboron Tetrachloride, B4Cl4. Inorg. Chem. 1963, 2, 396−400. (82) Rudolph, R. W. Mechanism of Addition of Diboron Tetrachloride to Unsaturated Organic Compounds. J. Am. Chem. Soc. 1967, 89, 4216−4217. (83) Ceron, P.; Finch, A.; Frey, J.; Kerrigan, J.; Parsons, T.; Urry, G.; Schlesinger, H. I. Diboron Tetrachloride and Tetrafluoride as Reagents for the Synthesis of Organoboron Compounds. II. The Behavior of the Diboron Tetrahalides toward Unsaturated Organic Compounds. J. Am. Chem. Soc. 1959, 81, 6368−6371. (84) Fox, W. B.; Wartik, T. Reaction of Diboron Tetrachloride with Aromatic Substances. J. Am. Chem. Soc. 1961, 83, 498−499. (85) Wartik, T.; Gassenheimer, B. Potentially Hazardous Reaction Between Dimethylmercury and Tetrachlorodiborane(4). Inorg. Chem. 1971, 10, 650. (86) Piers, W. E.; Irvine, G. J.; Williams, V. C. Highly Lewis Acidic Bifunctional Organoboranes. Eur. J. Inorg. Chem. 2000, 2131−2142. (87) Pubill-Ulldemolins, C.; Fernánez, E.; Bo, C.; Brown, J. M. Origins of Observed Reactivity and Specificity in the Addition of B2Cl4 and Analogues to Unsaturated Compounds. Org. Biomol. Chem. 2015, 13, 9619−9628. (88) Mohr, R. R.; Lipscomb, W. N. Structures and Energies of Diborane(4). Inorg. Chem. 1986, 25, 1053−1057. (89) Demachy, I.; Volatron, F. Hyperconjugation versus Steric Effects: Ab Initio Study of the B2D4 Systems (D = H, CH3, NH2, OH, F, Cl). J. Phys. Chem. 1994, 98, 10728−10734. (90) Vincent, M. A.; Schaefer, H. F. Diborane(4) (B2H4): the Boron Hydride Analog of Ethylene. J. Am. Chem. Soc. 1981, 103, 5677−5680. (91) Alkorta, I.; Soteras, I.; Elguero, J.; Del Bene, J. E. The BoronBoron Single Bond in Diborane(4) as a Non-Classical Electron Donor for Hydrogen Bonding. Phys. Chem. Chem. Phys. 2011, 13, 14026− 14032. (92) Chadha, R.; Ray, N. K. Theoretical Study of Reaction Paths. Diboration of Ethylene. J. Phys. Chem. 1982, 86, 3293−3294. (93) Chou, S.-L.; Lo, J.-I.; Peng, Y.-C.; Lin, M.-Y.; Lu, H.-C.; Cheng, B.-M.; Ogilvie, J. F. Identification of Diborane(4) with Bridging B-H-B Bonds. Chem. Sci. 2015, 6, 6872−6877. AW


Chemical Reviews

Review

(117) Snow, S. A.; Shimoi, M.; Ostler, C. D.; Thompson, B. K.; Kodama, G.; Parry, R. W. Metal Complexes of the Neutral Borane Adduct (B2H4·2P(CH3)3). Inorg. Chem. 1984, 23, 511−512. (118) Snow, S. A.; Kodama, G. Novel Coordination of a Neutral Borane Adduct to Nickel(0). Formation of Ni(CO)2[B2H4·2P(CH3)3]. Inorg. Chem. 1985, 24, 795−796. (119) Kaesz, H. D.; Fellmann, W.; Wilkes, G. R.; Dahl, L. F. A New Type of Electron-Deficient Compound. A Polyborane Hydridomanganese Carbonyl HMn3(CO)10(BH3)2. J. Am. Chem. Soc. 1965, 87, 2753−2755. (120) Sharmila, D.; Mondal, B.; Ramalakshmi, R.; Kundu, S.; Varghese, B.; Ghosh, S. First-Row Transition-Metal-Diborane and -Borylene Complexes. Chem. - Eur. J. 2015, 21, 5074−5083. (121) Wagner, A.; Kaifer, E.; Himmel, H.-J. Diborane(4)-Metal Bonding: Between Hydrogen Bridges and Frustrated Oxidative Addition. Chem. Commun. 2012, 48, 5277−5279. (122) Reddya, K. H. K.; Jemmis, E. D. Stabilization of Diborane(4) by Transition Metal Fragments and a Novel Metal to π Dewar-ChattDuncanson Model of Back Donation. Dalton Trans. 2013, 42, 10633− 10639. (123) Brotherton, R. J.; McCloskey, A. L.; Petterson, L. L.; Steinberg, H. Tetra-(amino)-Diborons. J. Am. Chem. Soc. 1960, 82, 6242−6245. (124) Brown, M. P.; Hunt, D. W.; Dann, A. E.; Silver, H. B. Transamination of Tetrakisdimethylaminodiboron with Aliphatic Diamines. J. Chem. Soc. 1962, 4648−4652. (125) Brubaker, G. L.; Shore, S. G. Boron Heterocycles. A Mass Spectrometric Investigation of Selected Heteronuclear Diborane(4) Ring Systems. Inorg. Chem. 1969, 8, 2804−2806. (126) Fusstetter, H.; Huffman, J. C.; Nöth, H.; Schaeffer, R. Contributions to Chemistry of Boron LXXXII. Crystal and MolecularStructure of B,B′-Bis(1,3-Dimethyl-1,3,2-Diazaborolidin-2-Yl). Z. Naturforsch., B: J. Chem. Sci. 1976, 31, 1441−1446. (127) Anton, K.; Nöth, H.; Pommerening, H. Beiträge zur Chemie des Bors, 140. Bor-, Aluminium- und Galliumhalogenid-Addukte einer Tetraaminodibor-Verbindung. Chem. Ber. 1984, 117, 2495−2503. (128) Malhotra, S. C. The Chemistry of Tetrakis(dimethylamino)diboron. Inorg. Chem. 1964, 3, 862−865. (129) Wann, D. A.; Robertson, H. E.; Bramham, G.; Bull, A. E. A.; Norman, N. C.; Russell, C. A.; Rankin, D. W. H. Unusual ChalcogenBoron Ring Compounds: the Gas-Phase Structures of 1,4B4S2(NMe2)4 and Related Molecules. Dalton Trans. 2009, 1446−1449. (130) Patton, J. T.; Feng, S. G. G.; Abboud, K. A. Chelating Diamide Group IV Metal Olefin Polymerization Catalysts. Organometallics 2001, 20, 3399−3405. (131) Brain, P. T.; Downs, A. J.; Maccallum, P.; Rankin, D. W. H.; Robertson, H. E.; Forsyth, G. A. The Molecular Structures of Gaseous Tetrakis(dimethylamino)-Diboron, B 2 (NMe 2 ) 4 , and Tetrakis(methoxy)diboron, B2(OMe)4, as Determined by Electron Diffraction. J. Chem. Soc., Dalton Trans. 1991, 1195−1200. (132) Xie, X.; Haddow, M. F.; Mansell, S. M.; Norman, N. C.; Russell, C. A. Diborane(4) Compounds with Bidentate Diamino Groups. Dalton Trans. 2012, 41, 2140−2147. (133) Müller, M.; Paetzold, P. Tri-tert-Butylazadiboriridine: a Molecule with a Basic Boron−Boron Bond. Coord. Chem. Rev. 1998, 176, 135−155. (134) Pospiech, S.; Bolte, M.; Lerner, H.-W.; Wagner, M. Ditopic tris(2-mercaptoimidazol-1-yl)borate Ligands and their Coordination Behavior Toward [Ru(p-cymene)]2+. Inorg. Chim. Acta 2011, 374, 566−571. (135) Weiss, A.; Hodgson, M. C.; Boyd, P. D. W.; Siebert, W.; Brothers, P. J. Diboryl and Diboranyl Porphyrin Complexes: Synthesis, Structural Motifs, and Redox Chemistry: Diborenyl Porphyrin or Diboranyl Isophlorin? Chem. - Eur. J. 2007, 13, 5982−5993. (136) Eckert, A. K.; Rodriguez-Morgade, M. S.; Torres, T. Molecular Diabolos: Synthesis of Subphthalocyanine-Based Diboranes. Chem. Commun. 2007, 4104−4106. (137) Ferguson, G.; Parvez, M.; Brint, R. P.; Power, D. C. M.; Spalding, T. R.; Lloyd, D. R. Notes. Synthesis, Crystal Structure and Gas-Phase Photoelectron Spectroscopic Study of B,B’-Bis(1,3-

(94) DePoy, R. E.; Kodama, G. Formation and Reaction Chemistry of Trimethylamine-Trimethylphosphine-Diborane(4). Inorg. Chem. 1988, 27, 1116−1118. (95) Paine, R. T. Phosphorus-Nitrogen-Boron Heteroring Systems. Preparation of Methylaminobis(difluorophosphine)diborane(4). J. Am. Chem. Soc. 1977, 99, 3884−3885. (96) Deever, W. R.; Lory, E. R.; Ritter, D. M. Bis(trifluorophosphine)diborane(4). Inorg. Chem. 1969, 8, 1263−1267. (97) Hertz, R. K.; Denniston, M. L.; Shore, S. G. Preparation and Characterization of B2H4·2P(CH3)3. Inorg. Chem. 1978, 17, 2673− 2674. (98) VanDoorne, W.; Cordes, A. W.; Hunt, G. W. Crystal and Molecular Structure of Bis(triphenylphosphine)-Diborane(4). Inorg. Chem. 1973, 12, 1686−1689. (99) Paine, R. T.; Parry, R. W. Preparation of Bis(halodifluorophosphine)-Diborane(4) Complexes. Inorg. Chem. 1975, 14, 689−691. (100) Deever, W. R.; Ritter, D. M. Diborane(4)-Bis(trifluorophosphine) Adduct. J. Am. Chem. Soc. 1967, 89, 5073. (101) Kameda, M.; Kodama, G. Cleavage Reaction of Pentaborane(9). Formation of a New Hypho Triborane Adduct. Inorg. Chem. 1980, 19, 2288−2292. (102) Kameda, M.; Kodama, G. Unsymmetrical Cleavage of Boranes by Bis(trimethlyphosphine)-Diborane(4). Formation of a Triboron Cation. J. Am. Chem. Soc. 1980, 102, 3647−3649. (103) Kameda, M.; Kodama, G. Reaction of Pentaborane(11) with Bis(trimethylphosphine)-Diborane(4). Inorg. Chem. 1982, 21, 1267− 1269. (104) Kameda, M.; Shimoi, M.; Kodama, G. Tetraborane(8) Adducts of Strongly Basic Phosphines. Inorg. Chem. 1984, 23, 3705−3709. (105) Kameda, M.; Driscoll, J. A.; Kodama, G. Formation and Reactions of Bis(trimethylphosphine)-Methyldiborane(4). Inorg. Chem. 1990, 29, 3791−3795. (106) Jock, C. P.; Kameda, M.; Kodama, G. Bis(trimethylphosphine)Diborane(4) as a Reagent for Borane Framework Expansion. Inorg. Chem. 1990, 29, 570−571. (107) Kameda, M.; Kodama, G. Synthesis of the Tris(trimethylphosphine)tetrahydrotriboron(1+) Cation. Inorg. Chem. 1997, 36, 4369−4371. (108) Shimoi, M.; Ikubo, S.; Kawano, Y.; Katoh, K.; Ogino, H. Synthesis and Structure of a Dinuclear Cobalt Complex Bridged by Nonsubstituted Borylene−Trimethylphosphine. J. Am. Chem. Soc. 1998, 120, 4222−4223. (109) Shimoi, M.; Katoh, K.; Kawano, Y.; Kodama, G.; Ogino, H. Fluxional Behavior of Chromium and Tungsten Complexes of Monodentate Bis(trimethylphosphine)diborane(4), [M(CO)5(η1B2H4·2PMe3)] (MCr, W): A Model Case for Alkane-Metal Complexes. J. Organomet. Chem. 2002, 659, 102−106. (110) Schulenberg, N.; Litters, S.; Kaifer, E.; Himmel, H.-J. Zinc Halide and Alkylzinc Complexes of a Neutral Doubly Base-Stabilized Diborane(4). Eur. J. Inorg. Chem. 2011, 2657−2661. (111) Piers, W. E. B−H Bond Activations in the Alkane Analogues H3B·PR3. Angew. Chem., Int. Ed. 2000, 39, 1923−1925. (112) Sakaki, S.; Kikuno, T. Reaction of BX2−BX2 (X = H or OH) with M(PH3)2 (M = Pd or Pt). A Theoretical Study of the Characteristic Features. Inorg. Chem. 1997, 36, 226−229. (113) Shimoi, M.; Katoh, K.; Tobita, H.; Ogino, H. Syntheses and Properties of Bis{bis(trimethylphosphine)tetrahydrodiboron}copper(+1) Halide (halide = chloride, iodide) and X-Ray Crystal Structure of the Iodide. Inorg. Chem. 1990, 29, 814−817. (114) Sivignon, G.; Fleurat-Lessard, P.; Onno, J.-M.; Volatron, F. Does Back-Bonding Involve Bonding Orbitals in Boryl Complexes? A Theoretical DFT Study. Inorg. Chem. 2002, 41, 6656−6661. (115) Katoh, K.; Shimoi, M.; Ogino, H. Syntheses and Structures of [M(CO)5{B2H4·2P(CH3)3}] and [M(CO)4{B2H4·2P(CH3)3}] (M = chromium, molybdenum, tungsten). Inorg. Chem. 1992, 31, 670−675. (116) Hata, M.; Kawano, Y.; Shimoi, M. Synthesis and Structure of a Dichromatetraborane Derivative [{(OC) 4 Cr} 2 (η 4 -H,H′,H″,H‴BH2BH2·PMe2CH2PMe2)]. Inorg. Chem. 1998, 37, 4482−4483. AX


Chemical Reviews

Review

dicyclohexyl-1,3,2-diazaborolidin-2-yl). J. Chem. Soc., Dalton Trans. 1986, 2283−2286. (138) Ciobanu, O.; Kaifer, E.; Enders, M.; Himmel, H.-J. Synthesis of a Stable B2H5+ Analogue by Protonation of a Double Base-Stabilized Diborane(4). Angew. Chem., Int. Ed. 2009, 48, 5538−5541. (139) Ciobanu, O.; Fuchs, A.; Reinmuth, M.; Lebkücher, A.; Kaifer, E.; Wadepohl, H.; Himmel, H.-J. Reactions between Boron and Magnesium Halides and the Bicyclic Guanidine hppH (1,3,4,6,7,8Hexahydro-2H-pyrimido[1,2-a]pyrimidine): Guanidinates with New Structural Motifs. Z. Anorg. Allg. Chem. 2010, 636, 543−550. (140) Paetzold, P.; Stanescu, C.; Stubenrauch, J. R.; Bienmüller, M.; Englert, U. 1-Azonia-2-boratanaphthalenes. Z. Anorg. Allg. Chem. 2004, 630, 2632−2640. (141) Nöth, H.; Knizek, J.; Ponikwar, W. A Boron−Boron Double Bond in the Dianions of Tetra(amino)diborates. Eur. J. Inorg. Chem. 1999, 1931−1937. (142) Weber, L.; Schnieder, M.; Lonnecke, P. Alkali Metal Reduction of 2-Halogeno- and 2-Thiolato-2,3-dihydro-1H-1,3,2-diazaboroles. J. Chem. Soc., Dalton Trans. 2001, 3459−3464. (143) Weber, L.; Domke, I.; Kahlert, J.; Stammler, H.-G. Chemical Oxidation of 1,3,2-Diazaboroles and 1,3,2-Diazaborolidines. Eur. J. Inorg. Chem. 2006, 2006, 3419−3424. (144) Brock, C. P.; Das, M. K.; Minton, R. P.; Niedenzu, K. Pyrazole Derivatives of Diborane(4). J. Am. Chem. Soc. 1988, 110, 817−822. (145) Novak, I.; Kovač, B. Boron Atom as an Electron Density Relay. Inorg. Chim. Acta 2008, 361, 1520−1523. (146) Schulenberg, N.; Jäkel, M.; Kaifer, E.; Himmel, H.-J. The Borane Complexes Htbo·BH3 and Htbn·BH3 (Htbo = 1,4,6Triazabicyclo[3.3.0]oct-4-ene, Htbn = 1,5,7-Triazabicyclo[4.3.0]non6-ene): Synthesis and Dehydrogenation to Dinuclear Boron Hydrides. Eur. J. Inorg. Chem. 2009, 4809−4819. (147) Haubold, W.; Zurmühl, K. Oxidation von Diboran(4)Verbindungen mit Chloraminen. Chem. Ber. 1980, 113, 2333−2341. (148) Abeler, G.; Nöth, H.; Schick, H. Beiträge zur Chemie des Bors, XLIII. Dimethylcarbamoyloxy- und Dimethylthiocarbamoylmercaptodiborane(4). Chem. Ber. 1968, 101, 3981−3986. (149) Schram, E. P. Aluminum-Aluminum Covalent Bonds. I. Hexamethyltris(dimethylamino)monoborontetraaluminum. Inorg. Chem. 1966, 5, 1291−1294. (150) Massey, A.; Thompson, N. Some Reactions of Tetra(dimethylamino)-Diboron. J. Inorg. Nucl. Chem. 1963, 25, 175−178. (151) Nöth, H.; Meister, W. Chemistry of Boron. XVII. Preparation of Dimethylaminodiborane Chlorides. Z. Naturforsch., B: J. Chem. Sci. 1962, 17, 714−718. (152) Becher, H. J.; Sawodny, W.; Nö th, H.; Meister, W. Schwingungsspektren und Strukturen von B2(OCH3)4 und B2[N(CH3)2]4. Z. Anorg. Allg. Chem. 1962, 314, 226−237. (153) Holliday, A. K.; Massey, A. G. Part I. Diboron TetrachlorideOlefin Compounds. Part I. Some Properties of Diboron Tetrachlorideethylene. J. Chem. Soc. 1960, 43−46. (154) Brotherton, R. J.; McCloskey, A. L.; Boone, J. L.; Manasevit, H. M. The Preparation and Properties of Some Tetraalkoxydiborons. J. Am. Chem. Soc. 1960, 82, 6245−6248. (155) Lesley, M. J. G.; Norman, N. C.; Rice, C. R.; Reger, D. L.; Little, C. A.; Lamba, J. J. S.; Brown, K. J.; Peters, J. C.; Thomas, C. J.; Sahasrabudhe, S. Main Group Compounds. Inorg. Synth. 2004, 34, 1− 48. (156) Nöth, H.; Meister, W. Beiträge zur Chemie des Bors, VI: Ü ber Subverbindungen des Bors. Hypoborsäure-tetrakis-dialkylamide und Hypoborsäure-ester. Chem. Ber. 1961, 94, 509−514. (157) Newsom, H. C.; Brotherton, R. J. Transesterification of Tetraalkoxydiborons. Inorg. Chem. 1963, 2, 423−424. (158) Petterson, L. L.; Brotherton, R. J. The Conversion of Tetrakis(dimethylamino)-diboron to Bis-(dimethylamino)-borane and Tris(dimethylamino)-borane by Thermal Decomposition. Inorg. Chem. 1963, 2, 423. (159) Baber, R. A.; Charmant, J. P. H.; Cook, A. J. R.; Farthing, N. E.; Haddow, M. F.; Norman, N. C.; Orpen, A. G.; Russell, C. A.; Slattery,

J. M. Primary Amido Substituted Diborane(4) Compounds and Imidodiborate(4) Anions. Dalton Trans. 2005, 3137−3139. (160) Alibadi, M. A. M.; Batsanov, A. S.; Bramham, G.; Charmant, J. P. H.; Haddow, M. F.; MacKay, L.; Mansell, S. M.; McGrady, J. E.; Norman, N. C.; Roffey, A.; Russell, C. A. 1,1- and 1,2-Isomers of the Diborane(4) Compound B2{1,2-(NH)2C6H4}2 and a TCNQ CoCrystal of the 1,1-Isomer. Dalton Trans. 2009, 5348−5354. (161) Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Rice, C. R. Diborane(4) Compounds Incorporating Thio- and Seleno-Carboranyl Groups. New J. Chem. 2000, 24, 837−839. (162) Moezzi, A.; Olmstead, M. M.; Power, P. P. Boron-Boron Double Bonding in the Species [B2R4]2‑: Synthesis and Structure of [{(Et2O)Li}2{Mes2BB(Mes)Ph}], a Diborane(4) Dianion Analog of a Substituted Ethylene. J. Am. Chem. Soc. 1992, 114, 2715−2717. (163) Jabbour, A.; Smoum, R.; Takrouri, K.; Shalom, E.; Zaks, B.; Steinberg, D.; Rubinstein, A.; Goldberg, I.; Katzhendler, J.; Srebnik, M. Pharmacologically Active Boranes. Pure Appl. Chem. 2006, 78, 1425− 1453. (164) Pospiech, S.; Brough, S.; Bolte, M.; Lerner, H.-W.; Bettinger, H. F.; Wagner, M. An Inorganic Propellane with Central B-B Bond. Chem. Commun. 2012, 48, 5886−5888. (165) Walton, J. C.; Brahmi, M. M.; Monot, J.; Fensterbank, L.; Malacria, M.; Curran, D. P.; Lacôte, E. Electron Paramagnetic Resonance and Computational Studies of Radicals Derived from Boron-Substituted N-Heterocyclic Carbene Boranes. J. Am. Chem. Soc. 2011, 133, 10312−10321. (166) Fırıncı, E.; Can Söyleyici, H.; Giziroğlu, E.; Temel, E.; Büyükgüngör, O.; Şahin, Y. Synthesis and Characterization of New Air Stable Primary Amido Substituted Diborane(4) Derivatives. Polyhedron 2010, 29, 1465−1468. (167) Braunschweig, H.; Ghosh, S.; Kupfer, T.; Radacki, K.; Wahler, J. High-Yield Synthesis of a Hybrid 2,3,4,5-Tetracarba-1,6-nidohexaborane(6) Cluster with an exo-Polyhedral Boracycle. Chem. Eur. J. 2011, 17, 4081−4084. (168) Hommer, H.; Nöth, H.; Knizek, J.; Ponikwar, W.; SchwenkKircher, H. Synthesis and Structures of Dimesityldiboranes(4). Eur. J. Inorg. Chem. 1998, 1519−1527. (169) Mitoraj, M. P.; Michalak, A. Multiple Boron−Boron Bonds in Neutral Molecules: An Insight from the Extended Transition State Method and the Natural Orbitals for Chemical Valence Scheme. Inorg. Chem. 2011, 50, 2168−2174. (170) Shoji, Y.; Matsuo, T.; Hashizume, D.; Fueno, H.; Tanaka, K.; Tamao, K. A Stable Doubly Hydrogen-Bridged Butterfly-Shaped Diborane(4) Compound. J. Am. Chem. Soc. 2010, 132, 8258−8260. (171) Shoji, Y.; Matsuo, T.; Hashizume, D.; Gutmann, M. J.; Fueno, H.; Tanaka, K.; Tamao, K. Boron−Boron σ-Bond Formation by TwoElectron Reduction of a H-Bridged Dimer of Monoborane. J. Am. Chem. Soc. 2011, 133, 11058−11061. (172) Knizek, J.; Krossing, I.; Nöth, H.; Ponikwar, W. Rearrangement of Bis(dimethylamino)bis(1-indenyl)diborane(4) into Bis(dimethylamino)bis(3-indenyl)diborane(4). Eur. J. Inorg. Chem. 1998, 505−509. (173) Grigsby, W. J.; Power, P. One-Electron Reductions of Organodiborane(4) Compounds: Singly Reduced Anions and Rearrangement Reactions. Chem. - Eur. J. 1997, 3, 368−375. (174) Brotherton, R. J.; McCloskey, A. L.; Manasevit, H. M. Preparation and Properties of 1,2-Diethyl-1,2-Bis-(Dimethylamino)and 1,2-Bis-(Dimethylamino)-1,2-Diphenyldiborons. Inorg. Chem. 1962, 1, 749−754. (175) Schluter, K.; Berndt, A. Persistent Tetraalkyldiboranes(4). Angew. Chem., Int. Ed. Engl. 1980, 19, 57−58. (176) Wakamiya, A.; Mori, K.; Araki, T.; Yamaguchi, S. A B−B BondContaining Polycyclic π-Electron System: Dithieno-1,2-dihydro-1,2diborin and Its Dianion. J. Am. Chem. Soc. 2009, 131, 10850−10851. (177) Araki, T.; Wakamiya, A.; Mori, K.; Yamaguchi, S. Elucidation of π-Conjugation Modes in Diarene-Fused 1,2-Dihydro-1,2-diborin Dianions. Chem. - Asian J. 2012, 7, 1594−1603. (178) Moezzi, A.; Olmstead, M. M.; Bartlett, R. A.; Power, P. P. Enhanced Thermal Stability in Organodiborane(4) Compounds: AY


Chemical Reviews

Review

(197) Clegg, W.; Elsegood, M. R. J.; Lawlor, F. J.; Norman, N. C.; Pickett, N. L.; Robins, E. G.; Scott, A. J.; Nguyen, P.; Taylor, N. J.; Marder, T. B. Structural Studies of Bis-Catecholate, Bis-Dithiocatecholate, and Tetraalkoxy Diborane(4) Compounds. Inorg. Chem. 1998, 37, 5289−5293. (198) Clegg, W.; Johann, T. R. F.; Marder, T. B.; Norman, N. C.; Orpen, A. G.; Peakman, T. M.; Quayle, M. J.; Rice, C. R.; Scott, A. J. Platinum-Catalysed 1,4-Diboration of 1,3-Dienes. J. Chem. Soc., Dalton Trans. 1998, 1431−1438. (199) Marder, T. B.; Norman, N. C.; Rice, C. R. Platinum Catalysed Diboration of Terminal Alkenes with Chiral Diborane(4) Compounds. Tetrahedron Lett. 1998, 39, 155−158. (200) Clegg, W.; Lawlor, F. J.; Lesley, G.; Marder, T. B.; Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Rice, C. R.; Scott, A. J.; Souza, F. E. S. Oxidative Addition of Boron−Boron, Boron−Chlorine and Boron− Bromine Bonds to Platinum(0). J. Organomet. Chem. 1998, 550, 183− 192. (201) Gao, M.; Thorpe, S. B.; Kleeberg, C.; Slebodnick, C.; Marder, T. B.; Santos, W. L. Structure and Reactivity of a Preactivated sp2-sp3 Diboron Reagent: Catalytic Regioselective Boration of α,β-Unsaturated Conjugated Compounds. J. Org. Chem. 2011, 76, 3997−4007. (202) Gao, M.; Thorpe, S. B.; Santos, W. L. sp2−sp3 Hybridized Mixed Diboron: Synthesis, Characterization, and Copper-Catalyzed βBoration of α,β-Unsaturated Conjugated Compounds. Org. Lett. 2009, 11, 3478−3481. (203) Asakawa, H.; Lee, K. H.; Lin, Z.; Yamashita, M. Facile Scission of Isonitrile Carbon-Nitrogen Triple Bond Using a Diborane(4) Reagent. Nat. Commun. 2014, 5, 4245. (204) Iwadate, N.; Suginome, M. Differentially Protected Diboron for Regioselective Diboration of Alkynes: Internal-Selective CrossCoupling of 1-Alkene-1,2-diboronic Acid Derivatives. J. Am. Chem. Soc. 2010, 132, 2548−2549. (205) Borner, C.; Kleeberg, C. Selective Synthesis of Unsymmetrical Diboryl Pt-II and Diaminoboryl Cu-I Complexes by B-B Activation of Unsymmetrical Diboranes(4) {pinB-B[(NR)2C6H4]}. Eur. J. Inorg. Chem. 2014, 2486−2489. (206) Borner, C.; Brandhorst, K.; Kleeberg, C. Selective B-B Bond Activation in an Unsymmetrical Diborane(4) by [(Me3P)4Rh−X] (X = Me, OtBu): a Switch of Mechanism? Dalton Trans. 2015, 44, 8600− 8604. (207) Perras, F. A.; Bryce, D. L. Boron-Boron J Coupling Constants are Unique Probes of Electronic Structure: a Solid-State NMR and Molecular Orbital Study. Chem. Sci. 2014, 5, 2428−2437. (208) Nguyen, P.; Dai, C.; Taylor, N. J.; Power, W. P.; Marder, T. B.; Pickett, N. L.; Norman, N. C. Lewis Base Adducts of Diboron Compounds: Molecular Structures of [B2(cat)2(4-picoline)] and [B2(cat)2(4-picoline)2] (cat = 1,2-O2C6H4). Inorg. Chem. 1995, 34, 4290−4291. (209) Cade, I. A.; Chau, W. Y.; Vitorica-Yrezabal, I.; Ingleson, M. J. 1,1/1,2 Isomerisation in Lewis Base Adducts of B2cat2. Dalton Trans. 2015, 44, 7506−7511. (210) Curtis, D.; Lesley, M. J. G.; Norman, N. C.; Orpen, A. G.; Starbuck, J. Phosphine Exchange Reactions Involving cis-[Pt(PPh3)2(Bcat)2] (cat = 1,2-O2C6H4) and the Oxidative Addition of 1,2-B2Cl2(NMe2)2 to Pt(0). J. Chem. Soc., Dalton Trans. 1999, 1687− 1694. (211) Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Rice, C. R. Three Sulfur-Containing Diborane(4) Compounds. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2000, 56, 440−444. (212) Marder, T. B.; Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Rice, C. R. Crystalline TCNQ and TCNE Adducts of the Diborane(4) Compounds B2(1,2-E2C6H4)2 (E = O or S). J. Chem. Soc., Dalton Trans. 1999, 2127−2132. (213) Kleeberg, C.; Crawford, A. G.; Batsanov, A. S.; Hodgkinson, P.; Apperley, D. C.; Cheung, M. S.; Lin, Z.; Marder, T. B. Spectroscopic and Structural Characterization of the CyNHC Adduct of B2pin2 in Solution and in the Solid State. J. Org. Chem. 2012, 77, 785−789. (214) Lee, K.-S.; Zhugralin, A. R.; Hoveyda, A. H. Efficient C-B Bond Formation Promoted by N-Heterocyclic Carbenes: Synthesis of

Synthesis and Structural Characterization of MeO(Mes)BB(Mes)OMe, Mes2BB(Mes)OMe, Mes2BB(Mes)Ph, and Mes2BB(Mes)CH2SiMe3 (Mes = 2,4,6-Me3C6H2). Organometallics 1992, 11, 2383−2388. (179) Wartik, T.; Apple, E. F. A New Modification of Boron Monoxide. J. Am. Chem. Soc. 1955, 77, 6400−6401. (180) Wartik, T.; Apple, E. F. The Reactions of Diboron Tetrachloride with Some Hydrogen Compounds of Non-Metallic Elements and with Dimethyl Sulfide. J. Am. Chem. Soc. 1958, 80, 6155−6158. (181) Baber, R. A.; Norman, N. C.; Orpen, A. G.; Rossi, J. The SolidState Structure of Diboronic Acid, B2(OH)4. New J. Chem. 2003, 27, 773−775. (182) Carmalt, C. J.; Clegg, W.; Cowley, A. H.; Lawlor, F. J.; Marder, T. B.; Norman, N. C.; Rice, C. R.; Sandoval, O. J.; Scott, A. J. Isolation and Structural Characterization of Novel Compounds Containing B4O2 Rings. Polyhedron 1997, 16, 2325−2328. (183) Loderer, D.; Nöth, H.; Pommerening, H.; Rattay, W.; Schick, H. Chemistry of Diborane(4) Derivatives: Mixed Tetraaminodiboranes(4) and Additions of Diborane(4) Derivatives to an Amino-iminoborane. Chem. Ber. 1994, 127, 1605−1611. (184) Ali, H. A.; Goldberg, I.; Srebnik, M. Tetra(pyrrolidino)diborane(4), [(C4H8N)2B]2, as a New Improved Alternative Synthetic Route to Bis(pinacolato)diborane(4) − Crystal Structures of the Intermediates. Eur. J. Inorg. Chem. 2002, 73−78. (185) Nöth, H. Beiträge zur Chemie des Bors. CLIII: Die Kristallund Molekülstruktur eines 1.3. 2-Dioxaborolan-2-yl-1.3. 2-dioxaborolans. Z. Naturforsch., B: J. Chem. Sci. 1984, 39, 1463−1466. (186) Brotherton, R. J.; Woods, W. G. U.S. Patent, 3009941, 1961. Brotherton, R. J.; Woods, W. G. Chem. Abstr. 1961, 55, 18011 (187) Lawlor, F. J.; Norman, N. C.; Pickett, N. L.; Robins, E. G.; Nguyen, P.; Lesley, G.; Marder, T. B.; Ashmore, J. A.; Green, J. C. BisCatecholate, Bis-Dithiocatecholate, and Tetraalkoxy Diborane(4) Compounds: Aspects of Synthesis and Electronic Structure. Inorg. Chem. 1998, 37, 5282−5288. (188) Anastasi, N. R.; Waltz, K. M.; Weerakoon, W. L.; Hartwig, J. F. A Short Synthesis of Tetraalkoxydiborane(4) Reagents. Organometallics 2003, 22, 365−369. (189) Braunschweig, H.; Guethlein, F. Transition-Metal-Catalyzed Synthesis of Diboranes(4). Angew. Chem., Int. Ed. 2011, 50, 12613− 12616. (190) Braunschweig, H.; Claes, C.; Guethlein, F. Dehydrocoupling of Catecholborane Catalyzed by Group 4 Compounds. J. Organomet. Chem. 2012, 706−707, 144−145. (191) Braunschweig, H.; Brenner, P.; Dewhurst, R. D.; Guethlein, F.; Jimenez-Halla, J. O. C.; Radacki, K.; Wolf, J.; Zöllner, L. Observation of Elementary Steps in the Catalytic Borane Dehydrocoupling Reaction. Chem. - Eur. J. 2012, 18, 8605−8609. (192) Shimada, S.; Batsanov, A. S.; Howard, J. A. K.; Marder, T. B. Formation of Aryl- and Benzylboronate Esters by Rhodium-Catalyzed C-H Bond Functionalization with Pinacolborane. Angew. Chem., Int. Ed. 2001, 40, 2168−2171. (193) Braunschweig, H.; Guethlein, F.; Mailänder, L.; Marder, T. B. Synthesis of Catechol-, Pinacol-, and Neopentylglycolborane through the Heterogeneous Catalytic B-B Hydrogenolysis of Diboranes(4). Chem. - Eur. J. 2013, 19, 14831−14835. (194) Wei, C. S.; Jimenez-Hoyos, C. A.; Videa, M. F.; Hartwig, J. F.; Hall, M. B. Origins of the Selectivity for Borylation of Primary over Secondary C-H Bonds Catalyzed by Cp*-Rhodium Complexes. J. Am. Chem. Soc. 2010, 132, 3078−3091. (195) Lam, W. H.; Lam, K. C.; Lin, Z. Y.; Shimada, S.; Perutz, R. N.; Marder, T. B. Theoretical Study of Reaction Pathways for the Rhodium Phosphine-Catalysed Borylation of C-H Bonds with Pinacolborane. Dalton Trans. 2004, 1556−1562. (196) Clegg, W.; Dai, C.; Lawlor, F. J.; Marder, T. B.; Nguyen, P.; Norman, N. C.; Pickett, N. L.; Power, W. P.; Scott, A. J. Lewis-Base Adducts of the Diborane(4) Compounds B2(1,2-E2C6H4)2 (E = O or S). J. Chem. Soc., Dalton Trans. 1997, 839−846. AZ


Chemical Reviews

Review

Anionic sp2-sp3 Diboron Compounds: Readily Accessible Boryl Nucleophiles. Chem. - Eur. J. 2015, 21, 7082−7098. (233) Bedford, R. B.; Brenner, P. B.; Carter, E.; Gallagher, T.; Murphy, D. M.; Pye, D. R. Iron-Catalyzed Borylation of Alkyl, Allyl, and Aryl Halides: Isolation of an Iron(I) Boryl Complex. Organometallics 2014, 33, 5940−5943. (234) Zheng, J. H.; Wang, Y. W.; Li, Z. H.; Wang, H. D. Application of a Nucleophilic Boryl Complex in the Frustrated Lewis Pair: Activation of H-H, B-H and CC Bonds with B(C6F5)3 and BorylBorate Lithium. Chem. Commun. 2015, 51, 5505−5508. (235) Asakawa, H.; Lee, K. H.; Furukawa, K.; Lin, Z.; Yamashita, M. Lowering the Reduction Potential of a Boron Compound by Means of the Substituent Effect of the Boryl Group: One-Electron Reduction of an Unsymmetrical Diborane(4). Chem. - Eur. J. 2015, 21, 4267−4271. (236) Luckert, S.; Eversheim, E.; Englert, U.; Wagner, T.; Paetzold, P. Reactions at the B−B Bond of Tri-tert-butylazadiboriridine NB2R3: Ring Extensions. Z. Anorg. Allg. Chem. 2001, 627, 1815−1823. (237) Biermann, K.; Paetzold, P. Reactions at the B−B Bond of Bis(trisyl)oxadiborirane: Ring Extensions. Z. Anorg. Allg. Chem. 2001, 627, 2313−2315. (238) Sahin, Y.; Ziegler, A.; Happel, T.; Meyer, H.; Bayer, M. J.; Pritzkow, H.; Massa, W.; Hofmann, M.; Schleyer, P. v. R.; Siebert, W.; Berndt, A. Two-Electron Homoaromatics with Heteroatom Bridges. J. Organomet. Chem. 2003, 680, 244−256. (239) Paetzold, P.; Géret-Baumgarten, L.; Boese, R. Bis(trisyl)oxadiborirane. Angew. Chem., Int. Ed. Engl. 1992, 31, 1040−1042. (240) Bühl, M.; Schaefer, H. F.; Schleyer, P. v. R.; Boese, R. On the BO Bond Length in Oxadiboriranes. Angew. Chem., Int. Ed. Engl. 1993, 32, 1154−1155. (241) Braunschweig, H.; Wagner, T. Synthesis and Structure of the First Transition Metal Borylene Complexes. Angew. Chem., Int. Ed. Engl. 1995, 34, 825−826. (242) Braunschweig, H.; Ganter, B. Convenient Synthesis of K[(C5H4Me)MnH(CO)2] and Reactions with Cl2B[N(SiMe3)2] and B2R2Cl2 (R = Me2N, Me3C). J. Organomet. Chem. 1997, 545−546, 163−167. (243) Braunschweig, H.; Müller, M. New Borylene Complexes of the Type [μ-BX{η5-C5H4Me)Mn(CO)2}2]: Substitution Reactions at the Metal-Coordinated Borylene Moiety. Chem. Ber. 1997, 130, 1295− 1298. (244) Braunschweig, H.; Colling, M.; Hu, C. H.; Radacki, K. From Classical to Nonclassical Metal-Boron Bonds: Synthesis of a Novel Metallaborane. Angew. Chem., Int. Ed. 2002, 41, 1359−1361. (245) Braunschweig, H. Transition Metal Complexes of Boron. Angew. Chem., Int. Ed. 1998, 37, 1786−1801. (246) Wrackmeyer, B. Metal Complexes Bearing Terminal Borylene Ligands. Angew. Chem., Int. Ed. 1999, 38, 771−772. (247) Braunschweig, H.; Dewhurst, R. D. Single, Double, Triple Bonds and Chains: The Formation of Electron-Precise B−B Bonds. Angew. Chem., Int. Ed. 2013, 52, 3574−3583. (248) Braunschweig, H.; Ganter, B.; Koster, M.; Wagner, T. Diboran(4)yl Groups as Ligands to Transition Metals. Chem. Ber. 1996, 129, 1099−1101. (249) Braunschweig, H.; Koster, M. Diborane(4)yl and Bridged Borylene Complexes from 1,2-Dipyrrolidino- and 1,2-Dipiperidinodiborane(4) Derivatives. J. Organomet. Chem. 1999, 588, 231−234. (250) Aldridge, S.; Coombs, D. L. Transition Metal Boryl and Borylene Complexes: Substitution and Abstraction Chemistry. Coord. Chem. Rev. 2004, 248, 535−559. (251) Braunschweig, H.; Koster, M.; Wang, R. Diborane(4)yl Complexes of Molybdenum and Ruthenium. Inorg. Chem. 1999, 38, 415−416. (252) Braunschweig, H.; Koster, M. Synthesis and Reactivity of Diborane(4)yl Complexes. Z. Naturforsch., B: J. Chem. Sci. 2002, 57, 483−487. (253) Braunschweig, H.; Damme, A.; Kupfer, T. Evidence for a Strong trans Influence of the Diboran(4)yl Ligand. Chem. - Eur. J. 2012, 18, 15927−15931.

Tertiary and Quaternary B-Substituted Carbons through Metal-Free Catalytic Boron Conjugate Additions to Cyclic and Acyclic α,βUnsaturated Carbonyls. J. Am. Chem. Soc. 2009, 131, 7253−7255. (215) Lee, K.-S.; Zhugralin, A. R.; Hoveyda, A. H. Efficient C-B Bond Formation Promoted by N-Heterocyclic Carbenes: Synthesis of Tertiary and Quaternary B-Substituted Carbons through Metal-Free Catalytic Boron Conjugate Additions to Cyclic and Acyclic α,βUnsaturated Carbonyls. J. Am. Chem. Soc. 2010, 132, 12766. (216) Pietsch, S.; Paul, U.; Cade, I. A.; Ingleson, M. J.; Radius, U.; Marder, T. B. Room Temperature Ring Expansion of N-Heterocyclic Carbenes and B-B Bond Cleavage of Diboron(4) Compounds. Chem. Eur. J. 2015, 21, 9018−9021. (217) Wurtemberger-Pietsch, S.; Radius, U.; Marder, T. B. 25 Years of N-Heterocyclic Carbenes: Activation of Both Main-Group ElementElement Bonds and NHCs Themselves. Dalton Trans. 2016, 45, 5880−5895. (218) Dewhurst, R. D.; Neeve, E. C.; Braunschweig, H.; Marder, T. B. sp2-sp3 Diboranes: Astounding Structural Variability and Mild Sources of Nucleophilic Boron for Organic Synthesis. Chem. Commun. 2015, 51, 9594−9607. (219) Palau-Lluch, G.; Sanz, X.; La Cascia, E.; Civit, M. G.; Miralles, N.; Cuenca, A. B.; Fernández, E. Organocatalytic Functionalisation Through Boron Chemistry. Pure Appl. Chem. 2015, 87, 181−193. (220) Cid, J.; Gulyás, H.; Carbo, J. J.; Fernández, E. Trivalent Boron Nucleophile as a New Tool in Organic Synthesis: Reactivity and Asymmetric Induction. Chem. Soc. Rev. 2012, 41, 3558−3570. (221) Gulyás, H.; Bonet, A.; Pubill-Ulldemolins, C.; Solé, C.; Cid, J.; Fernández, E. Nucleophilic Boron Strikes Back. Pure Appl. Chem. 2012, 84, 2219−2231. (222) Cid, J.; Carbo, J. J.; Fernández, E. Disclosing the Structure/ Activity Correlation in Trivalent Boron-Containing Compounds: A Tendency Map. Chem. - Eur. J. 2012, 18, 12794−12802. (223) Takahashi, K.; Ishiyama, T.; Miyaura, N. Addition and Coupling Reactions of Bis(pinacolato)diboron Mediated by CuCl in the Presence of Potassium Acetate. Chem. Lett. 2000, 982−983. (224) Takahashi, K.; Ishiyama, T.; Miyaura, N. A Borylcopper Species Generated from Bis(pinacolato)diboron and Its Additions to α,β-Unsaturated Carbonyl Compounds and Terminal Alkynes. J. Organomet. Chem. 2001, 625, 47−53. (225) Bonet, A.; Pubill-Ulldemolins, C.; Bo, C.; Gulyás, H.; Fernández, E. Transition-Metal-Free Diboration Reaction by Activation of Diboron Compounds with Simple Lewis Bases. Angew. Chem., Int. Ed. 2011, 50, 7158−7161. (226) Bonet, A.; Solé, C.; Gulyás, H.; Fernández, E. Asymmetric Organocatalytic Diboration of Alkenes. Org. Biomol. Chem. 2012, 10, 6621−6623. (227) Pubill-Ulldemolins, C.; Bonet, A.; Bo, C.; Gulyás, H.; Fernández, E. Activation of Diboron Reagents with Bronsted Bases and Alcohols: An Experimental and Theoretical Perspective of the Organocatalytic Boron Conjugate Addition Reaction. Chem. - Eur. J. 2012, 18, 1121−1126. (228) Pubill-Ulldemolins, C.; Bonet, A.; Gulyás, H.; Bo, C.; Fernández, E. Essential Role of Phosphines in Organocatalytic βBoration Reaction. Org. Biomol. Chem. 2012, 10, 9677−9682. (229) Sanz, X.; Lee, G. M.; Pubill-Ulldemolins, C.; Bonet, A.; Gulyás, H.; Westcott, S. A.; Bo, C.; Fernández, E. Metal-Free Borylative RingOpening of Vinyl Epoxides and Aziridines. Org. Biomol. Chem. 2013, 11, 7004−7010. (230) Solé, C.; Gulyás, H.; Fernández, E. Asymmetric Synthesis of αAmino Boronate Esters via Organocatalytic Pinacolboryl Addition to Tosylaldimines. Chem. Commun. 2012, 48, 3769−3771. (231) Kleeberg, C.; Dang, L.; Lin, Z.; Marder, T. B. A Facile Route to Aryl Boronates: Room-Temperature, Copper-Catalyzed Borylation of Aryl Halides with Alkoxy Diboron Reagents. Angew. Chem., Int. Ed. 2009, 48, 5350−5354. (232) Pietsch, S.; Neeve, E. C.; Apperley, D. C.; Bertermann, R.; Mo, F. Y.; Qiu, D.; Cheung, M. S.; Dang, L.; Wang, J. B.; Radius, U.; Lin, Z.; Kleeberg, C.; Marder, T. B. Synthesis, Structure, and Reactivity of BA


Chemical Reviews

Review

(254) Braunschweig, H.; Damme, A.; Kupfer, T. Conversion of transDiboran(4)yl Platinum Complexes into Their cis-Bisboryl Analogues. Chem. - Eur. J. 2013, 19, 14682−14686. (255) Braunschweig, H.; Damme, A.; Kupfer, T. Unexpected Bonding Mode of the Diboran(4)yl Ligand: Combining the Boryl Motif with a Dative Pt-B Interaction. Angew. Chem., Int. Ed. 2011, 50, 7179−7182. (256) Braunschweig, H.; Damme, A.; Kupfer, T. Diboran(4)yl Platinum(II) Complexes. Inorg. Chem. 2013, 52, 7822−7824. (257) Braunschweig, H.; Damme, A.; Dewhurst, R. D.; Vargas, A. Bond-Strengthening π Backdonation in a Transition-Metal π-Diborene Complex. Nat. Chem. 2013, 5, 115−121. (258) Brand, J.; Braunschweig, H.; Sen, S. S. BB and BE (E = N and O) Multiple Bonds in the Coordination Sphere of Late Transition Metals. Acc. Chem. Res. 2014, 47, 180−191. (259) Braunschweig, H.; Bertermann, R.; Damme, A.; Kupfer, T. A Dinuclear Platinum Complex Featuring the Diboran(4)-1,2-diyl Ligand in a μ2-Bridging Coordination Mode. Chem. Commun. 2013, 49, 2439−2441. (260) Herberhold, M.; Dörfler, U.; Wrackmeyer, B. The First 1,2Dibora-[2]ferrocenophane and Its Dynamic Behaviour in Solution. J. Organomet. Chem. 1997, 530, 117−120. (261) Lesley, M. J. G.; Mock, U.; Norman, N. C.; Orpen, A. G.; Rice, C. R.; Starbuck, J. Synthesis and X-Ray Structure of a [4]Ferrocenophane Containing a Boron-Boron Bond. J. Organomet. Chem. 1999, 582, 116−118. (262) Braunschweig, H.; Gross, M.; Kraft, M.; Kristen, M. O.; Leusser, D. [2]Borametallocenophanes of Zr and Hf: Synthesis, Structure, and Polymerization Activity. J. Am. Chem. Soc. 2005, 127, 3282−3283. (263) Braunschweig, H.; Gross, M.; Hammond, K.; Friedrich, M.; Kraft, M.; Oechsner, A.; Radacki, K.; Stellwag, S. [2]Borametallocenophanes of Group 4 Metals: Synthesis and Structure. Chem. - Eur. J. 2008, 14, 8972−8979. (264) Braunschweig, H.; Damme, A.; Kupfer, T. New [2]Boraferrocenophane and Diferrocenyldiborane(4) Derivatives. Eur. J. Inorg. Chem. 2010, 4423−4426. (265) Braunschweig, H.; Dörfler, R.; Mies, J.; Oechsner, A. Sterically Demanding Hetero-Substituted [2]Borametallocenophanes of Group IV Metals: Synthesis, Structure and Reactivity. Chem. - Eur. J. 2011, 17, 12101−12107. (266) Braunschweig, H.; Kupfer, T.; Mies, J.; Oechsner, A. Difluorenyl[2]borametallocenophanes of Group 4 Metals: Synthesis and Structure. Eur. J. Inorg. Chem. 2009, 2844−2850. (267) Braunschweig, H.; Lutz, M.; Radacki, K. Synthesis of ansa[2]Boracyclopentadienylcycloheptatrienylchromium and Its Reaction to the ansa-Platinabis(boryl) Complex by Oxidative Addition of the Boron-Boron Bond. Angew. Chem., Int. Ed. 2005, 44, 5647−5651. (268) Braunschweig, H.; Fuß, M.; Mohapatra, S. K.; Kraft, K.; Kupfer, T.; Lang, M.; Radacki, K.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Synthesis and Reactivity of Boron-, Silicon-, and Tin-Bridged ansaCyclopentadienyl−Cycloheptatrienyl Titanium Complexes (Troticenophanes). Chem. - Eur. J. 2010, 16, 11732−11743. (269) Aldridge, S.; Bresner, C. The Coordination Chemistry of Boryl and Borate Substituted Cyclopentadienyl Ligands. Coord. Chem. Rev. 2003, 244, 71−92. (270) Braunschweig, H.; Gruenewald, B.; Schwab, K.; Sigritz, R. 1,1′Diborylferrocenes from [2]Boraferrocenophanes by Boron-Boron Exchange. Eur. J. Inorg. Chem. 2009, 4860−4863. (271) Braunschweig, H.; Kupfer, T.; Lutz, M.; Radacki, K.; Seeler, F.; Sigritz, R. Metal-Mediated Diboration of Alkynes with [2]Borametalloarenophanes Under Stoichiometric, Homogeneous, and Heterogeneous Conditions. Angew. Chem., Int. Ed. 2006, 45, 8048− 8051. (272) Bauer, F.; Braunschweig, H.; Gruss, K.; Lambert, C.; Pandey, K. K.; Radacki, K.; Reitzenstein, D. Unexpected Generation of Diastereomers by Double Diboration of a Dialkyne. Chem. - Eur. J. 2011, 17, 5230−5233.

(273) Bauer, F.; Braunschweig, H.; Gruss, K.; Kupfer, T. Diboration of Dialkynes with [2]Boraferrocenophanes. Organometallics 2011, 30, 2869−2884. (274) Musgrave, R. A.; Russell, A. D.; Manners, I. Strained Ferrocenophanes. Organometallics 2013, 32, 5654−5667. (275) Braunschweig, H.; Dörfler, R.; Friedrich, M.; Kraft, M.; Oechsner, A. Catalytic Activity of [2]Borametallocenophanes. Z. Anorg. Allg. Chem. 2011, 637, 2125−2128. (276) Fischer, R. C.; Power, P. P. π-Bonding and the Lone Pair Effect in Multiple Bonds Involving Heavier Main Group Elements: Developments in the New Millennium. Chem. Rev. 2010, 110, 3877−3923. (277) Berndt, A.; Klusik, H.; Schluter, K. Radical-Anions from Organoboranes. J. Organomet. Chem. 1981, 222, C25−C27. (278) Power, P. P. Synthesis and Characterization of Compounds with Boron-Boron Double Bonds. Inorg. Chim. Acta 1992, 198−200, 443−447. (279) Moezzi, A.; Bartlett, R. A.; Power, P. P. Reduction of a Boron− Nitrogen 1,3-Butadiene Analogue: Evidence for a Strong B-B π-Bond. Angew. Chem., Int. Ed. Engl. 1992, 31, 1082−1083. (280) Grigsby, W. J.; Power, P. P. Comparison of B-B π-Bonding in Singly Reduced and Neutral Diborane (4) Derivatives: Isolation and Structure of [{Li(Et2O)2}{MeO(Mes)BB(Mes)OMe}]. Chem. Commun. 1996, 2235−2236. (281) Wang, Y.; Quillian, B.; Wei, P.; Wannere, C. S.; Xie, Y.; King, R. B.; Schaefer, H. F.; Schleyer, P. v. R.; Robinson, G. H. A Stable Neutral Diborene Containing a BB Double Bond. J. Am. Chem. Soc. 2007, 129, 12412−12413. (282) Braunschweig, H.; Dewhurst, R. D.; Hammond, K.; Mies, J.; Radacki, K.; Vargas, A. Ambient-Temperature Isolation of a Compound with a Boron-Boron Triple Bond. Science 2012, 336, 1420−1422. (283) Frenking, G.; Holzmann, N. A Boron-Boron Triple Bond. Science 2012, 336, 1394−1395. (284) Braunschweig, H.; Dewhurst, R. D. Boron-Boron Multiple Bonding: From Charged to Neutral and Back Again. Organometallics 2014, 33, 6271−6277. (285) Bohnke, J.; Braunschweig, H.; Constantinidis, P.; Dellermann, T.; Ewing, W. C.; Fischer, I.; Hammond, K.; Hupp, F.; Mies, J.; Schmitt, H. C.; Vargas, A. Experimental Assessment of the Strengths of B-B Triple Bonds. J. Am. Chem. Soc. 2015, 137, 1766−1769. (286) Li, S.-D.; Zhai, H.-J.; Wang, L.-S. B2(BO)22− Diboronyl Diborene: A Linear Molecule with a Triple Boron−Boron Bond. J. Am. Chem. Soc. 2008, 130, 2573−2579. (287) Shoji, Y.; Kaneda, S.; Fueno, H.; Tanaka, K.; Tamao, K.; Hashizume, D.; Matsuo, T. An Isolable Diborane(4) Compound with Terminal B-H Bonds: Structural Characteristics and Electronic Properties. Chem. Lett. 2014, 43, 1587−1589. (288) Braunschweig, H.; Damme, A.; Jimenez-Halla, J. O. C.; Kupfer, T.; Radacki, K. Phosphine Adducts of 1,2-Dibromo-1,2-dimesityldiborane(4): Between Bridging Halides and Rearrangement Processes. Angew. Chem., Int. Ed. 2012, 51, 6267−6271. (289) Bissinger, P.; Braunschweig, H.; Damme, A.; Dewhurst, R. D.; Kupfer, T.; Radacki, K.; Wagner, K. Generation of a CarbeneStabilized Bora-borylene and its Insertion into a C-H Bond. J. Am. Chem. Soc. 2011, 133, 19044−19047. (290) Braunschweig, H.; Damme, A.; Dewhurst, R. D.; Kramer, T.; Kupfer, T.; Radacki, K.; Siedler, E.; Trumpp, A.; Wagner, K.; Werner, C. Quaternizing Diboranes(4): Highly Divergent Outcomes and an Inorganic Wagner−Meerwein Rearrangement. J. Am. Chem. Soc. 2013, 135, 8702−8707. (291) Braunschweig, H.; Damme, A.; Kupfer, T. Synthesis of a Bicyclic Diborane by Selective Boron Carbon Bond Formation. Chem. Commun. 2013, 49, 2774−2776. (292) Arnold, N.; Braunschweig, H.; Damme, A.; Dewhurst, R. D.; Pentecost, L.; Radacki, K.; Stellwag-Konertz, S.; Thiess, T.; Trumpp, A.; Vargas, A. New Outcomes of Lewis Base Addition to Diboranes(4): Electronic Effects Override Strong Steric Disincentives. Chem. Commun. 2016, 52, 4898−4901. BB


Chemical Reviews

Review

Diboryl Complex with, and without, Metathesis of Boron-Boron and Metal-Carbon Bonds. J. Am. Chem. Soc. 1995, 117, 4403−4404. (312) Iverson, C. N.; Smith, M. R. Mechanistic Investigation of Stoichiometric Alkyne Insertion into Pt-B Bonds and Related Chemistry Bearing on the Catalytic Diborylation of Alkynes Mediated by Platinum(II) Diboryl Complexes. Organometallics 1996, 15, 5155− 5165. (313) Ishiyama, T.; Matsuda, N.; Miyaura, N.; Suzuki, A. Platinum(0)-Catalyzed Diboration of Alkynes. J. Am. Chem. Soc. 1993, 115, 11018−11019. (314) Ishiyama, T.; Yamamoto, M.; Miyaura, N. Diboration of Alkenes with Bis(pinacolato)diboron Catalyzed by a Platinum(0) Complex. Chem. Commun. 1997, 689−690. (315) Mann, G.; John, K. D.; Baker, R. T. Platinum-Catalyzed Diboration Using a Commercially Available Catalyst: Diboration of Aldimines to α-Aminoboronate Esters. Org. Lett. 2000, 2, 2105−2108. (316) Iverson, C. N.; Smith, M. R. Efficient Olefin Diboration by a Base-Free Platinum Catalyst. Organometallics 1997, 16, 2757−2759. (317) Braunschweig, H.; Bertermann, R.; Brenner, P.; Burzler, M.; Dewhurst, R. D.; Radacki, K.; Seeler, F. trans-[Pt(BCat′)Me(PCy3)2]: An Experimental Case Study of Reductive Elimination Processes in Pt−Boryls through Associative Mechanisms. Chem. - Eur. J. 2011, 17, 11828−11837. (318) Braunschweig, H.; Damme, A. Thermodynamic Control of Oxidative Addition and Reductive Elimination Processes in cisBis(dimethoxyboryl)-Bis(tricyclohexylphosphine)Platinum(II). Chem. Commun. 2013, 49, 5216−5218. (319) Baker, R. T.; Calabrese, J. C.; Westcott, S. A.; Nguyen, P.; Marder, T. B. Insertion of Alkenes into Rhodium-Boron Bonds. J. Am. Chem. Soc. 1993, 115, 4367−4368. (320) Clegg, W.; Lawlor, F. J.; Marder, T. B.; Nguyen, P.; Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Rice, C. R.; Robins, E. G.; Scott, A. J.; Souza, F. E. S.; Stringer, G.; Whittell, G. R. Boron−Boron Bond Oxidative Addition to Rhodium(I) and Iridium(I) Centres. J. Chem. Soc., Dalton Trans. 1998, 301−310. (321) Dai, C.; Stringer, G.; Marder, T. B.; Baker, R. T.; Scott, A. J.; Clegg, W.; Norman, N. C. Oxidative Addition of a B-B Bond by an Iridium(I) Complex: Molecular Structure of mer-cis-[Ir(PMe3)3Cl(Bcat)2]. Can. J. Chem. 1996, 74, 2026−2031. (322) Marder, T. B.; Norman, N. C.; Rice, C. R.; Robins, E. G. Reaction Between Rhodium(III) Bisboryls and Diborane(4) Compounds: Evidence for a σ-Bond Metathesis Process. Chem. Commun. 1997, 53−54. (323) Dai, C.; Stringer, G.; Marder, T. B.; Scott, A. J.; Clegg, W.; Norman, N. C. Synthesis and Characterization of Rhodium(I) Boryl and Rhodium(III) Tris(Boryl) Compounds: Molecular Structures of [(PMe3)4Rh(B(cat))] and fac-[(PMe3)3Rh(B(cat))3] (cat = 1,2O2C6H4). Inorg. Chem. 1997, 36, 272−273. (324) Campian, M. V.; Harris, J. L.; Jasim, N.; Perutz, R. N.; Marder, T. B.; Whitwood, A. C. Comparisons of Photoinduced Oxidative Addition of B-H, B-B, and Si-H Bonds at Rhodium(η 5 cyclopentadienyl)phosphine Centers. Organometallics 2006, 25, 5093−5104. (325) Dai, C.; Stringer, G.; Corrigan, J. F.; Taylor, N. J.; Marder, T. B.; Norman, N. C. Synthesis and Molecular Structure of the Paramagnetic Co(II) Bis(boryl) Complex [Co(PMe3)3(Bcat)2 (cat = 1,2,-O2C6H4). J. Organomet. Chem. 1996, 513, 273−275. (326) Adams, C. J.; Baber, R. A.; Batsanov, A. S.; Bramham, G.; Charmant, J. P. H.; Haddow, M. F.; Howard, J. A. K.; Lam, W. H.; Lin, Z.; Marder, T. B.; Norman, N. C.; Orpen, A. G. Synthesis and Reactivity of Cobalt Boryl Complexes. Dalton Trans. 2006, 1370− 1373. (327) Rickard, C. E. F.; Roper, W. R.; Williamson, A.; Wright, L. J. Synthesis and Structures of cis- and trans-[Os(Bcat) (aryl)(CO)2(PPh3)2]: Compounds of Relevance to the Metal-Catalyzed Hydroboration Reaction and the Metal-Mediated Borylation of Arenes. Angew. Chem., Int. Ed. 1999, 38, 1110−1113. (328) Rickard, C. E. F.; Roper, W. R.; Williamson, A.; Wright, L. J. Reactions of cis and trans Bcat, Aryl Osmium Complexes (cat = 1,2-

(293) Weinmann, W.; Pritzkow, H.; Siebert, W. Synthese, Deprotonierung und Ringerweiterung eines 2,3-Diboratetralins. Chem. Ber. 1994, 127, 611−613. (294) Lesley, M. J. G.; Norman, N. C.; Orpen, A. G.; Starbuck, J. Synthetic Routes to Cyclic and Unsymmetric Diborane(4) Compounds. New J. Chem. 2000, 24, 115−117. (295) Rendtorff, N.; Castro, E. Molecular Mechanics Study of Cyclic and Unsymmetrical Diborane (4) Compounds. Russ. J. Gen. Chem. 2003, 73, 1881−1883. (296) Xie, X.; Haddow, M. F.; Mansell, S. M.; Norman, N. C.; Russell, C. A. New Polycyclic Borazine Species. Chem. Commun. 2011, 47, 3748−3750. (297) Xie, X.; Adams, C. J.; Al-Ibadi, M. A. M.; McGrady, J. E.; Norman, N. C.; Russell, C. A. A Polycyclic Borazine Radical Cation: [1,2-B2{1,2-(MeN)2C6H4}2]•+. Chem. Commun. 2013, 49, 10364− 10366. (298) Klusik, H.; Berndt, A. A Boron-Boron One-Electron π-Bond. Angew. Chem., Int. Ed. Engl. 1981, 20, 870−871. (299) Bissinger, P.; Braunschweig, H.; Damme, A.; Kupfer, T.; Krummenacher, I.; Vargas, A. Boron Radical Cations from the Facile Oxidation of Electron-Rich Diborenes. Angew. Chem., Int. Ed. 2014, 53, 5689−5693. (300) Hubner, A.; Diehl, A. M.; Diefenbach, M.; Endeward, B.; Bolte, M.; Lerner, H. W.; Holthausen, M. C.; Wagner, M. Confirmed by XRay Crystallography: the BB One-Electron σ Bond. Angew. Chem., Int. Ed. 2014, 53, 4832−4835. (301) Barbeyron, R.; Benedetti, E.; Cossy, J.; Vasseur, J. J.; Arseniyadis, S.; Smietana, M. Recent Developments in Alkyne Borylations. Tetrahedron 2014, 70, 8431−8452. (302) Chadha, R.; Ray, N. K. MNDO Study of Reaction Paths: Diboration of Acetylene. Theoret. Chim. Acta 1982, 60, 573−578. (303) Ishiyama, T.; Matsuda, N.; Murata, M.; Ozawa, F.; Suzuki, A.; Miyaura, N. Platinum(0)-Catalyzed Diboration of Alkynes with Tetrakis(alkoxo)diborons: An Efficient and Convenient Approach to cis-Bis(boryl)alkenes. Organometallics 1996, 15, 713−720. (304) Cui, Q.; Musaev, D. G.; Morokuma, K. Density Functional Study on the Mechanism of Palladium(0)-Catalyzed Thioboration Reaction of Alkynes. Differences between Pd(0) and Pt(0) Catalysts and between Thioboration and Diboration. Organometallics 1998, 17, 1383−1392. (305) Cui, Q.; Musaev, D. G.; Morokuma, K. Why Do Pt(PR3)2 Complexes Catalyze the Alkyne Diboration Reaction, but Their Palladium Analogues Do Not? A Density Functional Study. Organometallics 1998, 17, 742−751. (306) Cui, Q.; Musaev, D. G.; Morokuma, K. Molecular Orbital Study of the Mechanism of Platinum(0)-Catalyzed Alkene and Alkyne Diboration Reactions. Organometallics 1997, 16, 1355−1364. (307) Burks, H. E.; Liu, S.; Morken, J. P. Development, Mechanism, and Scope of the Palladium-Catalyzed Enantioselective Allene Diboration. J. Am. Chem. Soc. 2007, 129, 8766−8773. (308) Clegg, W.; Scott, A. J.; Lesley, G.; Marder, T. B.; Norman, N. C. The Product of Catalysed Diboration of Bis(4-methoxyphenyl)ethyne by Bis(pinacolato-O,O’)diboron. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1996, 52, 1989−1991. (309) Clegg, W.; Scott, A. J.; Lesley, G.; Marder, T. B.; Norman, N. C. The Products of Catalysed Diboration of Bis(p-tolyl)ethyne and of 4-Cyanophenyl-Ethyne by Bis(catecholato-O,O’)diboron. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1996, 52, 1991−1995. (310) Lesley, G.; Nguyen, P.; Taylor, N. J.; Marder, T. B.; Scott, A. J.; Clegg, W.; Norman, N. C. Synthesis and Characterization of Platinum(II)-Bis(boryl) Catalyst Precursors for Diboration of Alkynes and Diynes: Molecular Structures of cis-[(PPh3)2Pt(B-4-Butcat)2], cis[(PPh3)2Pt(Bcat)2], cis-[(dppe)Pt(Bcat)2], cis-[(dppb)Pt(Bcat)2], (E)(4-MeOC6H4)C(Bcat)CH(Bcat), (Z)-(C6H5)C(Bcat)C(C6H5) (Bcat), and (Z,Z)-(4-MeOC6H4)C(Bcat)C(Bcat)C(Bcat)C(4MeOC6H4) (Bcat) (cat = 1,2-O2C6H4; dppe = Ph2PCH2CH2PPh2; dppb = Ph2P(CH2)4PPh2). Organometallics 1996, 15, 5137−5154. (311) Iverson, C. N.; Smith, M. R. Reactivity of Organoplatinum Complexes with C6H4O2B−BO2C6H4: Syntheses of a Platinum BC


Chemical Reviews

Review

Diboration of Alkenes: Mechanistic Insights. Chem. Commun. 2007, 3380−3382. (348) Corberán, R.; Lillo, V.; Mata, J. A.; Fernández, E.; Peris, E. Enantioselective Preparation of a Chiral-at-Metal Cp*Ir(NHC) Complex and Its Application in the Catalytic Diboration of Olefins. Organometallics 2007, 26, 4350−4353. (349) Tran, B. L.; Adhikari, D.; Fan, H.; Pink, M.; Mindiola, D. J. Facile Entry to 3d Late Transition Metal Boryl Complexes. Dalton Trans. 2010, 39, 358−360. (350) Adhikari, D.; Mossin, S.; Basuli, F.; Dible, B. R.; Chipara, M.; Fan, H.; Huffman, J. C.; Meyer, K.; Mindiola, D. J. A Dinuclear Ni(I) System Having a Diradical Ni2N2 Diamond Core Resting State: Synthetic, Structural, Spectroscopic Elucidation, and Reductive Bond Splitting Reactions. Inorg. Chem. 2008, 47, 10479−10490. (351) Dang, L.; Zhao, H.; Lin, Z.; Marder, T. B. DFT Studies of Alkene Insertions into Cu−B Bonds in Copper(I) Boryl Complexes. Organometallics 2007, 26, 2824−2832. (352) Dang, L.; Zhao, H.; Lin, Z.; Marder, T. B. Understanding the Higher Reactivity of B2cat2 Versus B2pin2 in Copper(I)-Catalyzed Alkene Diboration Reactions. Organometallics 2008, 27, 1178−1186. (353) Dang, L.; Lin, Z.; Marder, T. B. DFT Studies on the Borylation of α, β-Unsaturated Carbonyl Compounds Catalyzed by Phosphine Copper(I) Boryl Complexes and Observations on the Interconversions Between O- and C-Bound Enolates of Cu, B, and Si. Organometallics 2008, 27, 4443−4454. (354) Bonet, A.; Solé, C.; Gulyás, H.; Fernández, E. Organocatalytic versus Iron-Assisted β-Boration of Electron-Deficient Olefins. Chem. Asian J. 2011, 6, 1011−1014. (355) Zhao, H.; Dang, L.; Marder, T. B.; Lin, Z. DFT Studies on the Mechanism of the Diboration of Aldehydes Catalyzed by Copper(I) Boryl Complexes. J. Am. Chem. Soc. 2008, 130, 5586−5594. (356) Yoshida, H.; Kawashima, S.; Takemoto, Y.; Okada, K.; Ohshita, J.; Takaki, K. Copper-Catalyzed Borylation Reactions of Alkynes and Arynes. Angew. Chem., Int. Ed. 2012, 51, 235−238. (357) Zhu, Y.; Chen, C.-H.; Fafard, C. M.; Foxman, B. M.; Ozerov, O. V. Net Heterolytic Cleavage of B−H and B−B Bonds Across the N−Pd Bond in a Cationic (PNP)Pd Fragment. Inorg. Chem. 2011, 50, 7980−7987. (358) Chambers, C.; Holliday, A. K. 625. The Reaction of Diboron Tetrahalides with Acetylene. Part I. The Preparation and Properties of 1,2-Bisdichloroborylethylene. J. Chem. Soc. 1965, 3459−3462. (359) Siebert, W.; Hildenbrand, M.; Hornbach, P.; Karger, G.; Pritzkow, H. 1,2- and 1,1-Diborylalkenes. Z. Naturforsch., B: J. Chem. Sci. 1989, 44, 1179−1186. (360) Klusik, H.; Pues, C.; Berndt, A. 1,1-Diboration of 1(Trimethylsilyl)alkynes. Z. Naturforsch., B: J. Chem. Sci. 1984, 39, 1042−1045. (361) Yoshida, H.; Okada, K.; Kawashima, S.; Tanino, K.; Ohshita, J. Platinum-Catalyzed Diborylation of Arynes: Synthesis and Reaction of 1,2-Diborylarenes. Chem. Commun. 2010, 46, 1763−1765. (362) Thomas, R. Ll.; Souza, F. E. S.; Marder, T. B. Highly Efficient Monophosphine Platinum Catalysts for Alkyne Diboration. J. Chem. Soc., Dalton Trans. 2001, 1650−1656. (363) Grirrane, A.; Corma, A.; Garcia, H. Stereoselective Single (Copper) or Double (Platinum) Boronation of Alkynes Catalyzed by Magnesia-Supported Copper Oxide or Platinum Nanoparticles. Chem. - Eur. J. 2011, 17, 2467−2478. (364) Alonso, F.; Moglie, Y.; Pastor-Pérez, L.; Sepúlveda-Escribano, A. Solvent- and Ligand-free Diboration of Alkynes and Alkenes Catalyzed by Platinum Nanoparticles on Titania. ChemCatChem 2014, 6, 857−865. (365) Khan, A.; Asiri, A. M.; Kosa, S. A.; Garcia, H.; Grirrane, A. Catalytic Stereoselective Addition to Alkynes. Borylation or Silylation Promoted by Magnesia-Supported Iron Oxide and cis-Diboronation or Silaboration by Supported Platinum Nanoparticles. J. Catal. 2015, 329, 401−412. (366) Chen, Q.; Zhao, J.; Ishikawa, Y.; Asao, N.; Yamamoto, Y.; Jin, T. Remarkable Catalytic Property of Nanoporous Gold on Activation

O2C6H4). Bis(Bcat) Complexes of Osmium and Ruthenium and a Structural Comparison of cis and trans Isomers of Os(Bcat)I(CO)2(PPh3)2. Organometallics 2000, 19, 4344−4355. (329) He, X.; Hartwig, J. F. Boryls Bound to Iron Carbonyl. Structure of a Rare Bis(boryl) Complex, Synthesis of the First Anionic Boryl, and Reaction Chemistry That Includes the Synthetic Equivalent of Boryl Anion Transfer. Organometallics 1996, 15, 400−407. (330) Hartwig, J. F.; He, X. Reactivity of Tungstenocene with B−B and B−H Bonds versus C−H Bonds. Angew. Chem., Int. Ed. Engl. 1996, 35, 315−317. (331) Kerr, A.; Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Rice, C. R.; Timms, P. L.; Whittell, G. R.; Marder, T. B. Preparation and Structure of cis-[Pt(BF2)2(PPh3)2]: the First Crystallographically Characterised Complex Containing the BF2 Ligand. Chem. Commun. 1998, 319−320. (332) Lu, N.; Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Timms, P. L.; Whittell, G. R. Transition Metal Complexes Incorporating the BF2 Ligand Formed by Oxidative Addition of the B−B Bond in B2F4. Dalton Trans. 2000, 4032−4037. (333) Charmant, J. P. H.; Fan, C.; Norman, N. C.; Pringle, P. G. Synthesis and Reactivity of Dichloroboryl Complexes of Platinum(II). Dalton Trans. 2007, 114−123. (334) Lu, N.; Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Timms, P. L.; Whittell, G. R. Transition Metal Complexes Incorporating the BF2 Ligand Formed by Oxidative Addition of the B−B Bond in B2F4. J. Chem. Soc., Dalton Trans. 2000, 4032−4037. (335) Baker, R. T.; Nguyen, P.; Marder, T. B.; Westcott, S. A. Transition Metal Catalyzed Diboration of Vinylarenes. Angew. Chem., Int. Ed. Engl. 1995, 34, 1336−1338. (336) Dai, C.; Robins, E. G.; Yufit, D. S.; Howard, J. A. K.; Marder, T. B.; Scott, A. J.; Clegg, W. Rhodium Catalysed Diboration of Unstrained Internal Alkenes and a New and General Route to Zwitterionic [L2Rh(η6-catBcat)] (cat = 1,2-O2C6H4) Complexes. Chem. Commun. 1998, 1983−1984. (337) Morgan, J. B.; Miller, S. P.; Morken, J. P. Rhodium-Catalyzed Enantioselective Diboration of Simple Alkenes. J. Am. Chem. Soc. 2003, 125, 8702−8703. (338) Trudeau, S.; Morgan, J. B.; Shrestha, M.; Morken, J. P. RhCatalyzed Enantioselective Diboration of Simple Alkenes: Reaction Development and Substrate Scope. J. Org. Chem. 2005, 70, 9538− 9544. (339) Ramírez, J.; Segarra, A. M.; Fernández, E. Metal Promoted Asymmetry in the 1,2-Diboroethylarene Synthesis: Diboration Versus Dihydroboration. Tetrahedron: Asymmetry 2005, 16, 1289−1294. (340) Pubill-Ulldemolins, C.; Poyatos, M.; Bo, C.; Fernández, E. Rhodium-NHC Complexes Mediate Diboration Versus Dehydrogenative Borylation of Cyclic Olefins: a Theoretical Explanation. Dalton Trans. 2013, 42, 746−752. (341) Beletskaya, I.; Pelter, A. Hydroborations Catalysed by Transition Metal Complexes. Tetrahedron 1997, 53, 4957−5026. (342) Pelz, N. F.; Woodward, A. R.; Burks, H. E.; Sieber, J. D.; Morken, J. P. Palladium-Catalyzed Enantioselective Diboration of Prochiral Allenes. J. Am. Chem. Soc. 2004, 126, 16328−16329. (343) Laitar, D. S.; Mueller, P.; Sadighi, J. P. Efficient Homogeneous Catalysis in the Reduction of CO2 to CO. J. Am. Chem. Soc. 2005, 127, 17196−17197. (344) Laitar, D. S.; Tsui, E. Y.; Sadighi, J. P. Catalytic Diboration of Aldehydes via Insertion into the Copper-Boron Bond. J. Am. Chem. Soc. 2006, 128, 11036−11037. (345) Lillo, V.; Fructos, M. R.; Ramírez, J.; Braga, A. A. C.; Maseras, F.; Díaz-Requejo, M. M.; Perez, P. J.; Fernández, E. A Valuable, Inexpensive Cu(I)/N-Heterocyclic Carbene Catalyst for the Selective Diboration of Styrene. Chem. - Eur. J. 2007, 13, 2614−2621. (346) Ramírez, J.; Sanau, M.; Fernández, E. Gold(0) Nanoparticles for Selective Catalytic Diboration. Angew. Chem., Int. Ed. 2008, 47, 5194−5197. (347) Lillo, V.; Mas-Marza, E.; Segarra, A. M.; Carbo, J. J.; Bo, C.; Peris, E.; Fernández, E. Palladium-NHC Complexes Do Catalyse the BD


Chemical Reviews

Review

of Diborons for Direct Diboration of Alkynes. Org. Lett. 2013, 15, 5766−5769. (367) Morgan, J. B.; Morken, J. P. Catalytic Enantioselective Hydrogenation of Vinyl Bis(boronates). J. Am. Chem. Soc. 2004, 126, 15338−15339. (368) Ramírez, J.; Fernández, E. Convenient Synthesis of α,αDifluorinated Carbonyl Compounds from Alkynes Through a FluoroDeboronation Process. Synthesis 2005, 1698−1700. (369) Ramírez, J.; Fernández, E. One-Pot Synthesis of α,αDifluoroimines from Alkynes Through Tandem Catalytic Diboration/Fluorination/Imination Reaction. Tetrahedron Lett. 2007, 48, 3841−3845. (370) Brown, S. D.; Armstrong, R. W. Synthesis of Tetrasubstituted Ethylenes on Solid Support via Resin Capture. J. Am. Chem. Soc. 1996, 118, 6331−6332. (371) Wu, J.-S.; Lin, C.-T.; Wang, C.-L.; Cheng, Y.-J.; Hsu, C.-S. New Angular-Shaped and Isomerically Pure Anthradithiophene with Lateral Aliphatic Side Chains for Conjugated Polymers: Synthesis, Characterization, and Implications for Solution-Prossessed Organic Field-Effect Transistors and Photovoltaics. Chem. Mater. 2012, 24, 2391−2399. (372) Prokopcova, H.; Ramírez, J.; Fernández, E.; Kappe, C. O. Microwave-Assisted One-Pot Diboration/Suzuki Cross-Couplings. A Rapid Route to Tetrasubstituted Alkenes. Tetrahedron Lett. 2008, 49, 4831−4835. (373) Carson, M. W.; Giese, M. W.; Coghlan, M. J. An Intra/ Intermolecular Suzuki Sequence to Benzopyridyloxepines Containing Geometrically Pure Exocyclic Tetrasubstituted Alkenes. Org. Lett. 2008, 10, 2701−2704. (374) Jiao, J.; Hyodo, K.; Hu, H.; Nakajima, K.; Nishihara, Y. Selective Synthesis of Multisubstituted Olefins Utilizing gem- and vicDiborylated Vinylsilanes Prepared by Silylborylation of an Alkynylboronate and Diborylation of Alkynylsilanes. J. Org. Chem. 2014, 79, 285− 295. (375) Yoshida, H.; Asatsu, Y.; Mimura, Y.; Ito, Y.; Ohshita, J.; Takaki, K. Three-Component Coupling of Arynes and Organic Bromides. Angew. Chem., Int. Ed. 2011, 50, 9676−9679. (376) Ishiyama, T.; Yamamoto, M.; Miyaura, N. A Synthesis of (E)(1-Organo-1-alkenyl)boronates by the Palladium-Catalyzed CrossCoupling Reaction of (E)-1,2-bis(Boryl)-1-alkenes with Organic Halides: a Formal Carboboration of Alkynes via the DiborationCoupling Sequence. Chem. Lett. 1996, 1117−1118. (377) Kraft, P.; Tochtermann, W. Synthesis of Medium and Large Ring Compounds. XXXVII. Synthesis and Olfactory Properties of (Z)5,6-Dimethylcyclododec-5-en-1-one and (Z)-(±)-5,6-Dimethylcyclododec-5-en-1-ol. Liebigs Ann. Chem. 1994, 1994, 827−830. (378) Xu, L.; Zhang, S.; Li, P. Boron-Selective Reactions as Powerful Tools for Modular Synthesis of Diverse Complex Molecules. Chem. Soc. Rev. 2015, 44, 8848−8858. (379) Anderson, K. M.; Lesley, M. J. G.; Norman, N. C.; Orpen, A. G.; Starbuck, J. The Platinum Catalysed Diboration of Alkynes Using 1,2-B2Cl2(NMe2)2: Formation of 1-Azonia-2-Borata-5-Borole Derivatives. New J. Chem. 1999, 23, 1053−1055. (380) Ali, H. A.; El Aziz Al Quntar, A.; Goldberg, I.; Srebnik, M. Platinum(0)-Catalyzed Diboration of Alkynylboronates and Alkynylphosphonates with Bis(pinacolato)diborane(4): Molecular Structures of [((Me4C2O2)B)(C6H5)CC(P(O)(OC2H5)2)(B(O2C2Me4))] and [((Me4C2O2)B)(C4H9)CC(B(O2C2Me4))2]. Organometallics 2002, 21, 4533−4539. (381) Nagao, K.; Ohmiya, H.; Sawamura, M. Anti-Selective Vicinal Silaboration and Diboration of Alkynoates through Phosphine Organocatalysis. Org. Lett. 2015, 17, 1304−1307. (382) Morinaga, A.; Nagao, K.; Ohmiya, H.; Sawamura, M. Synthesis of 1,1-Diborylalkenes through a Brønsted Base Catalyzed Reaction between Terminal Alkynes and Bis(pinacolato)diboron. Angew. Chem., Int. Ed. 2015, 54, 15859−15862. (383) Nagashima, Y.; Hirano, K.; Takita, R.; Uchiyama, M. TransDiborylation of Alkynes: Pseudo-Intramolecular Strategy Utilizing a Propargylic Alcohol Unit. J. Am. Chem. Soc. 2014, 136, 8532−8535.

(384) Yun, J. Copper(I)-Catalyzed Boron Addition Reactions of Alkynes with Diboron Reagents. Asian J. Org. Chem. 2013, 2, 1016− 1025. (385) Fujihara, T.; Semba, K.; Terao, J.; Tsuji, Y. Regioselective Transformation of Akynes Catalyzed by a Copper Hydride or Boryl Copper Species. Catal. Sci. Technol. 2014, 4, 1699−1709. (386) Yoshida, H. Copper Catalysis for Synthesizing Main-Group Organometallics Containing B, Sn or Si. Chem. Rec. 2016, 16, 419− 434. (387) Yoshida, H. Borylation of Alkynes under Base/Coinage Metal Catalysis: Some Recent Developments. ACS Catal. 2016, 6, 1799− 1811. (388) Iida, A.; Saito, S.; Sasamori, T.; Yamaguchi, S. Borylated Dibenzoborepin: Synthesis by Skeletal Rearrangement and Photochromism Based on Bora-Nazarov Cyclization. Angew. Chem., Int. Ed. 2013, 52, 3760−3764. (389) Nakagawa, N.; Hatakeyama, T.; Nakamura, M. Iron-Catalyzed Diboration and Carboboration of Alkynes. Chem. - Eur. J. 2015, 21, 4257−4261. (390) Yoshimura, A.; Takamachi, Y.; Han, L.-B.; Ogawa, A. Organosulfide-Catalyzed Diboration of Terminal Alkynes under Light. Chem. - Eur. J. 2015, 21, 13930−13933. (391) Zeldin, M.; Gatti, A.; Wartik, T. Stereochemical Investigations of the Addition of Diboron Tetrachloride to Unsaturated Organic Molecules. J. Am. Chem. Soc. 1967, 89, 4217−4218. (392) Ahmed, L.; Castillo, J.; Saulys, D.; Morrison, J. Reactivity of the Diboron Tetrahalides. Diboration of Ethylene with Diboron Tetrabromide and Thermal Decomposition and Ligand Exchanges of Diboron Tetrabromide and Diboron Tetrachloride in Carbon Tetrabromide and Carbon Tetrachloride. Inorg. Chem. 1992, 31, 706− 710. (393) Rosen, A.; Zeldin, M. Chemistry of Tetrachlorodiborane(4) 1. Reactions with Cyclic Olefin. J. Organomet. Chem. 1971, 31, 319−328. (394) Coyle, T. D.; Ritter, J. J. Organometallic Aspects of Diboron Chemistry. Advances in Organometallic Chemistry; Academic Press: Cambridge, 1972; pp 237−272. (395) Haubold, W.; Stanzl, K. Addition of Diborontetrahalides to Unsaturated-Hydrocarbons. Chem. Ber. 1978, 111, 2108−2112. (396) Ritter, J. J.; Coyle, T. D.; Bellama, J. M. Reactions of Diboron Tetrahalides with Haloolefins - Formation of Poly(Dihaloboryl)Ethanes. J. Organomet. Chem. 1971, 29, 175−184. (397) Dewhurst, R. D.; Marder, T. B. Cascades of Catalytic Selectivity. Nat. Chem. 2014, 6, 279−280. (398) Fernández, E.; Guiry, P. J.; Connole, K. P. T.; Brown, J. M. Quinap and Congeners: Atropos PN ligands for Asymmetric Catalysis. J. Org. Chem. 2014, 79, 5391−5400. (399) Kliman, L. T.; Mlynarski, S. N.; Morken, J. P. Pt-Catalyzed Enantioselective Diboration of Terminal Alkenes with B2(pin)2. J. Am. Chem. Soc. 2009, 131, 13210−13211. (400) Coombs, J. R.; Morken, J. P. Catalytic Enantioselective Functionalization of Unactivated Terminal Alkenes. Angew. Chem., Int. Ed. 2016, 55, 2636−2649. (401) Toribatake, K.; Nishiyama, H. Asymmetric Diboration of Terminal Alkenes with a Rhodium Catalyst and Subsequent Oxidation: Enantioselective Synthesis of Optically Active 1,2-Diols. Angew. Chem., Int. Ed. 2013, 52, 11011−11015. (402) Toribatake, K.; Miyata, S.; Naganawa, Y.; Nishiyama, H. Asymmetric Synthesis of Optically Active 3-Amino-1,2-diols from NAcyl-Protected Allylamines via Catalytic Diboration with Rh[bis(oxazolinyl)phenyl] Catalysts. Tetrahedron 2015, 71, 3203−3208. (403) Miller, S. P.; Morgan, J. B.; Nepveux, F. J.; Morken, J. P. Catalytic Asymmetric Carbohydroxylation of Alkenes by a Tandem Diboration/Suzuki Cross-Coupling/Oxidation Reaction. Org. Lett. 2004, 6, 131−133. (404) Kalendra, D. M.; Duenes, R. A.; Morken, J. P. Regioselective Homologation of Bis(boronate) Intermediates Derived from Rhodium-Catalyzed Diboration of Simple Alkenes. Synlett 2005, 1749− 1751. BE


Chemical Reviews

Review

(405) Coombs, J. R.; Zhang, L.; Morken, J. P. Enantiomerically Enriched Tris(boronates): Readily Accessible Conjunctive Reagents for Asymmetric Synthesis. J. Am. Chem. Soc. 2014, 136, 16140−16143. (406) Blaisdell, T. P.; Caya, T. C.; Zhang, L.; Sanz-Marco, A.; Morken, J. P. Hydroxyl-Directed Stereoselective Diboration of Alkenes. J. Am. Chem. Soc. 2014, 136, 9264−9267. (407) Coombs, J. R.; Haeffner, F.; Kliman, L. T.; Morken, J. P. Scope and Mechanism of the Pt-Catalyzed Enantioselective Diboration of Monosubstituted Alkenes. J. Am. Chem. Soc. 2013, 135, 11222−11231. (408) Mlynarski, S. N.; Schuster, C. H.; Morken, J. P. Asymmetric Synthesis from Terminal Alkenes by Cascades of Diboration and Cross-Coupling. Nature 2014, 505, 386−390. (409) Blaisdell, T. P.; Morken, J. P. Hydroxyl-Directed CrossCoupling: A Scalable Synthesis of Debromohamigeran E and Other Targets of Interest. J. Am. Chem. Soc. 2015, 137, 8712−8715. (410) Ramírez, J.; Corberan, R.; Sanau, M.; Peris, E.; Fernández, E. Unprecedented Use of Silver(I) N-Heterocyclic Carbene Complexes for the Catalytic Preparation of 1,2-Bis(boronate) Esters. Chem. Commun. 2005, 3056−3058. (411) Pubill-Ulldemolins, C.; Bo, C.; Mata, J. A.; Fernández, E. Perceptible Influence of Pd and Pt Heterocyclic Carbene−Pyridyl Complexes in Catalytic Diboration of Cyclic Alkenes. Chem. - Asian J. 2010, 5, 261−264. (412) Carter, C. A. G.; Vogels, C. M.; Harrison, D. J.; Gagnon, M. K. J.; Norman, D. W.; Langler, R. F.; Baker, R. T.; Westcott, S. A. MetalCatalyzed Hydroboration and Diboration of Thiocarbonyls and Vinyl Sulfides. Organometallics 2001, 20, 2130−2132. (413) Penno, D.; Lillo, V.; Koshevoy, I. O.; Sanaú, M.; Ubeda, M. A.; Lahuerta, P.; Fernández, E. Multifaceted Palladium Catalysts Towards the Tandem Diboration−Arylation Reactions of Alkenes. Chem. - Eur. J. 2008, 14, 10648−10655. (414) Penno, D.; Estevan, F.; Fernández, E.; Hirva, P.; Lahuerta, P.; Sanaú, M.; Ú beda, M. A. Dinuclear Ortho-Metalated Palladium(II) Compounds with N,N- and N,O-Donor Bridging Ligands. Synthesis of New Palladium(III) Complexes. Organometallics 2011, 30, 2083− 2094. (415) Cuenca, A. B.; Zigon, N.; Duplan, V.; Hoshino, M.; Fujita, M.; Fernández, E. Undeniable Confirmation of the syn-Addition Mechanism for Metal-Free Diboration Using the Crystalline Sponge Method. Chem. - Eur. J. 2016, 22, 4723−4726. (416) Miralles, N.; Cid, J.; Cuenca, A. B.; Carbo, J. J.; Fernández, E. Mixed Diboration of Alkenes in a Metal-Free Context. Chem. Commun. 2015, 51, 1693−1696. (417) Fang, L.; Yan, L.; Haeffner, F.; Morken, J. P. CarbohydrateCatalyzed Enantioselective Alkene Diboration: Enhanced Reactivity of 1,2-Bonded Diboron Complexes. J. Am. Chem. Soc. 2016, 138, 2508− 2511. (418) Lillo, V.; Mata, J.; Ramírez, J.; Peris, E.; Fernández, E. Catalytic Diboration of Unsaturated Molecules with Platinum(0)-NHC: Selective Synthesis of 1,2-Dihydroxysulfones. Organometallics 2006, 25, 5829−5831. (419) Corberan, R.; Ramírez, J.; Poyatos, M.; Peris, E.; Fernández, E. Coinage Metal Complexes with N-Heterocyclic Carbene Ligands as Selective Catalysts in Diboration Reaction. Tetrahedron: Asymmetry 2006, 17, 1759−1762. (420) Maderna, A.; Pritzkow, H.; Siebert, W. Hexaborylbenzene and Tetraborylethene Derivatives. Angew. Chem., Int. Ed. Engl. 1996, 35, 1501−1503. (421) Bluhm, M.; Maderna, A.; Pritzkow, H.; Bethke, S.; Gleiter, R.; Siebert, W. Synthesis of Tetraborylethenes and 1,1,1′,1′-Tetra- and Hexaborylethanes; Electronic Interactions in Tetraborylethenes and 1,1,1′,1′-Tetraborylethanes, and HF-SCF Calculations. Eur. J. Inorg. Chem. 1999, 1693−1700. (422) Hyodo, K.; Suetsugu, M.; Nishihara, Y. Diborylation of Alkynyl MIDA Boronates and Sequential Chemoselective Suzuki−Miyaura Couplings: A Formal Carboborylation of Alkynes. Org. Lett. 2014, 16, 440−443. (423) Nguyen, P.; Coapes, R. B.; Woodward, A. D.; Taylor, N. J.; Burke, J. M.; Howard, J. A. K.; Marder, T. B. Rhodium(I) Catalysed

Diboration of (E)-Styrylboronate Esters: Molecular Structures of (E)p-MeO−C6 H4 −CHCH−B(1,2-O2C 6H 4) and p-MeO−C 6H 4− CH2C{B(1,2-O2C6H4)}3. J. Organomet. Chem. 2002, 652, 77−85. (424) Zhang, L.; Huang, Z. Synthesis of 1,1,1-Tris(boronates) from Vinylarenes by Co-Catalyzed Dehydrogenative Borylations-Hydroboration. J. Am. Chem. Soc. 2015, 137, 15600−15603. (425) Haubold, W.; Stanzl, K. Die addition von tetrahalogenodiboran(4)-molekülen an diene. J. Organomet. Chem. 1979, 174, 141− 147. (426) Ishiyama, T.; Yamamoto, M.; Miyaura, N. Platinum(0)Catalyzed Diboration of Alka-1,3-dienes with Bis(pinacolato)diboron. Chem. Commun. 1996, 2073−2074. (427) Schuster, C. H.; Li, B.; Morken, J. P. Modular Monodentate Oxaphospholane Ligands: Utility in Highly Efficient and Enantioselective 1,4-Diboration of 1,3-Dienes. Angew. Chem., Int. Ed. 2011, 50, 7906−7909. (428) Burks, H. E.; Kliman, L. T.; Morken, J. P. Asymmetric 1,4Dihydroxylation of 1,3-Dienes by Catalytic Enantioselective Diboration. J. Am. Chem. Soc. 2009, 131, 9134−9135. (429) Hong, K.; Morken, J. P. Catalytic Enantioselective Diboration of Cyclic Dienes. A Modified Ligand with General Utility. J. Org. Chem. 2011, 76, 9102−9108. (430) Lam, H. W. TADDOL-Derived Phosphonites, Phosphites, and Phosphoramidites in Asymmetric Catalysis. Synthesis 2011, 2011− 2043. (431) Poe, S. L.; Morken, J. P. A Boron-Based Synthesis of the Natural Product (+)-trans-Dihydrolycoricidine. Angew. Chem., Int. Ed. 2011, 50, 4189−4192. (432) Yu, Z. Y.; Ely, R. J.; Morken, J. P. Synthesis of (+)-Discodermolide by Catalytic Stereoselective Borylation Reactions. Angew. Chem., Int. Ed. 2014, 53, 9632−9636. (433) Morgan, J. B.; Morken, J. P. Platinum-Catalyzed Tandem Diboration/Asymmetric Allylboration: Access to Nonracemic Functionalized 1,3-Diols. Org. Lett. 2003, 5, 2573−2575. (434) Yu, C.-M.; Youn, J.; Yoon, S.-K.; Hong, Y.-T. A Highly Stereoselective Sequential Allylic Transfer Reaction of Diene with Diboronyl Reagent and Aldehydes Promoted by Nickel Catalyst. Org. Lett. 2005, 7, 4507−4510. (435) Cho, H. Y.; Morken, J. P. Diastereoselective Construction of Functionalized Homoallylic Alcohols by Ni-Catalyzed DiboronPromoted Coupling of Dienes and Aldehydes. J. Am. Chem. Soc. 2008, 130, 16140−16141. (436) Cho, H. Y.; Morken, J. P. Ni-Catalyzed Borylative DieneAldehyde Coupling: The Remarkable Effect of P(SiMe3)3. J. Am. Chem. Soc. 2010, 132, 7576−7577. (437) Ely, R. J.; Morken, J. P. Ni(0)-Catalyzed 1,4-Selective Diboration of Conjugated Dienes. Org. Lett. 2010, 12, 4348−4351. (438) Kliman, L. T.; Mlynarski, S. N.; Ferris, G. E.; Morken, J. P. Catalytic Enantioselective 1,2-Diboration of 1,3-Dienes: Versatile Reagents for Stereoselective Allylation. Angew. Chem., Int. Ed. 2012, 51, 521−524. (439) Ishiyama, T.; Kitano, T.; Miyaura, N. Platinum(0)-Catalyzed Diboration of Allenes with Bis(pinacolato)diboron. Tetrahedron Lett. 1998, 39, 2357−2360. (440) Wang, M.; Cheng, L.; Wu, Z. Theoretical Studies on the Reaction Mechanism of Platinum-Catalyzed Diboration of Allenes. Organometallics 2008, 27, 6464−6471. (441) Guo, X.; Nelson, A. K.; Slebodnick, C.; Santos, W. L. Regioand Chemoselective Diboration of Allenes with Unsymmetrical Diboron: Formation of Vinyl and Allyl Boronic Acid Derivatives. ACS Catal. 2015, 5, 2172−2176. (442) Yang, F.-Y.; Cheng, C.-H. Unusual Diboration of Allenes Catalyzed by Palladium Complexes and Organic Iodides: A New Efficient Route to Biboronic Compounds. J. Am. Chem. Soc. 2001, 123, 761−762. (443) Kleinnijenhuis, R. A.; Timmer, B. J. J.; Lutteke, G.; Smits, J. M. M.; de Gelder, R.; van Maarseveen, J. H.; Hiemstra, H. Formal Synthesis of Solanoeclepin A: Enantioselective Allene Diboration and BF


Chemical Reviews

Review

Intramolecular [2 + 2] Photocycloaddition for the Construction of the Tricyclic Core. Chem. - Eur. J. 2016, 22, 1266−1269. (444) Woodward, A. R.; Burks, H. E.; Chan, L. M.; Morken, J. P. Concatenated Catalytic Asymmetric Allene Diboration/Allylation/ Functionalization. Org. Lett. 2005, 7, 5505−5507. (445) Le, H.; Kyne, R. E.; Brozek, L. A.; Morken, J. P. Catalytic Enantioselective Allyl−Allyl Cross-Coupling with a Borylated Allylboronate. Org. Lett. 2013, 15, 1432−1435. (446) Sieber, J. D.; Morken, J. P. Sequential Pd-Catalyzed Asymmetric Allene Diboration/α-Aminoallylation. J. Am. Chem. Soc. 2006, 128, 74−75. (447) Pelz, N. F.; Morken, J. P. Modular Asymmetric Synthesis of 1,2-Diols by Single-Pot Allene Diboration/Hydroboration/CrossCoupling. Org. Lett. 2006, 8, 4557−4559. (448) Zhao, H.; Lin, Z.; Marder, T. B. Density Functional Theory Studies on the Mechanism of the Reduction of CO2 to CO Catalyzed by Copper(I) Boryl Complexes. J. Am. Chem. Soc. 2006, 128, 15637− 15643. (449) Enthaler, S. Zinc-Catalyzed Deoxygenation of Sulfoxides to Sulfides Applying [B(Pin)]2 as Deoxygenation Reagents. Catal. Lett. 2012, 142, 1306−1311. (450) Kokatla, H. P.; Thomson, P. F.; Bae, S.; Doddi, V. R.; Lakshman, M. K. Reduction of Amine N-Oxides by Diboron Reagents. J. Org. Chem. 2011, 76, 7842−7848. (451) Londregan, A. T.; Piotrowski, D. W.; Xiao, J. Rapid and Selective In Situ Reduction of Pyridine-N-oxides with Tetrahydroxydiboron. Synlett 2013, 24, 2695−2700. (452) Zhang, G. Y.; Xie, Y. J.; Wang, Z. K.; Liu, Y.; Huang, H. M. Diboron as a Reductant for Nickel-Catalyzed Reductive Coupling: Rational Design and Mechanistic Studies. Chem. Commun. 2015, 51, 1850−1853. (453) Doi, R.; Ohashi, M.; Ogoshi, S. Copper-Catalyzed Reaction of Trifluoromethylketones with Aldehydes via a Copper Difluoroenolate. Angew. Chem., Int. Ed. 2016, 55, 341−344. (454) McIntosh, M. L.; Moore, C. M.; Clark, T. B. Copper-Catalyzed Diboration of Ketones: Facile Synthesis of Tertiary α-Hydroxyboronate Esters. Org. Lett. 2010, 12, 1996−1999. (455) Moore, C. M.; Medina, C. R.; Cannamela, P. C.; McIntosh, M. L.; Ferber, C. J.; Roering, A. J.; Clark, T. B. Facile Formation of βHydroxyboronate Esters by a Cu-Catalyzed Diboration/Matteson Homologation Sequence. Org. Lett. 2014, 16, 6056−6059. (456) Guan, W. Y.; Michael, A. K.; McIntosh, M. L.; Koren-Selfridge, L.; Scott, J. P.; Clark, T. B. Stereoselective Formation of Trisubstituted Vinyl Boronate Esters by the Acid-Mediated Elimination of αHydroxyboronate Esters. J. Org. Chem. 2014, 79, 7199−7204. (457) Cuenca, A. B.; Cid, J.; Garcia-López, D.; Carbo, J. J.; Fernández, E. Unsymmetrical 1,1-Diborated Multisubstituted sp3Carbons Formed via a Metal-Free Concerted-Asynchronous Mechanism. Org. Biomol. Chem. 2015, 13, 9659−9664. (458) Cuenca, A. B.; Cid, J.; Garcia-López, D.; Carbo, J. J.; Fernández, E. Correction: Unsymmetrical 1,1-Diborated Multisubstituted sp3-Carbons Formed via a Metal-Free Concerted-Asynchronous Mechanism. Org. Biomol. Chem. 2015, 13, 11772. (459) Cameron, T. M.; Baker, R. T.; Westcott, S. A. Metal-Catalysed Multiple Boration of Ketimines. Chem. Commun. 1998, 2395−2396. (460) Lee, C. H.; Laitar, D. S.; Mueller, P.; Sadighi, J. P. Generation of a Doubly Bridging CO2 Ligand and Deoxygenation of CO2 by an (NHC)Ni(0) Complex. J. Am. Chem. Soc. 2007, 129, 13802−13803. (461) Hong, K.; Morken, J. P. Catalytic Enantioselective One-pot Aminoborylation of Aldehydes: A Strategy for Construction of Nonracemic α-Amino Boronates. J. Am. Chem. Soc. 2013, 135, 9252−9254. (462) Hommer, H.; Nöth, H.; Sachdev, H.; Schmidt, M.; Schwenk, H. Contributions to the Chemistry of Boron, 231. Synthesis and Structures of Borylated Hydrazines. Chem. Ber. 1995, 128, 1187−1194. (463) Braunschweig, H.; Kupfer, T. Stoichiometric and Homogeneous-Catalytic Diboration of the N:N Double Bond of Azobenzene. J. Am. Chem. Soc. 2008, 130, 4242−4243.

(464) Chen, J.-Y.; Su, M.-D. Diboration of the EE Double Bond by [2]Metallocenophanes (E = N, P, As, Sb, and Bi): A Theoretical Study. Organometallics 2010, 29, 5812−5820. (465) Abu Ali, H.; Goldberg, I.; Srebnik, M. Addition Reactions of Bis(pinacolato)diborane(4) to Carbonyl Enones and Synthesis of (pinacolato)2BCH2B and (pinacolato)2BCH2CH2B by Insertion and Coupling. Organometallics 2001, 20, 3962−3965. (466) Abu Ali, H.; Goldberg, I.; Kaufmann, D.; Burmeister, C.; Srebnik, M. Novel C1-Bridged Bisboronate Derivatives by Insertion of Diazoalkanes into Bis(pinacolato)diborane(4). Organometallics 2002, 21, 1870−1876. (467) Wommack, A. J.; Kingsbury, J. S. On the Scope of the PtCatalyzed Srebnik Diborylation of Diazoalkanes. An Efficient Approach to Chiral Tertiary Boronic Esters and Alcohols via BStabilized Carbanions. Tetrahedron Lett. 2014, 55, 3163−3166. (468) Kajiwara, T.; Takeda, N.; Sasamori, T.; Tokitoh, N. Unprecedented Insertion Reaction of a Silylene into a B−B Bond and Generation of a Novel Borylsilyl Anion by Boron-Metal Exchange Reaction of the Resultant Diborylsilane. Chem. Commun. 2004, 2218− 2219. (469) Kajiwara, T.; Takeda, N.; Sasamori, T.; Tokitoh, N. Synthesis of Alkali Metal Salts of Borylsilyl Anions Utilizing Highly Crowded Silylboranes and Their Properties. Organometallics 2008, 27, 880−893. (470) Li, H.; Wang, L.; Zhang, Y.; Wang, J. B. Transition-Metal-Free Synthesis of Pinacol Alkylboronates from Tosylhydrazones. Angew. Chem., Int. Ed. 2012, 51, 2943−2946. (471) Li, H.; Zhang, Y.; Wang, J. B. Reaction of Diazo Compounds with Organoboron Compounds. Synthesis 2013, 45, 3090−3098. (472) Li, H.; Shangguan, X. H.; Zhang, Z. K.; Huang, S.; Zhang, Y.; Wang, J. B. Formal Carbon Insertion of N-Tosylhydrazone into B−B and B−Si Bonds: gem-Diborylation and gem-Silylborylation of sp3 Carbon. Org. Lett. 2014, 16, 448−451. (473) Bauer, F.; Braunschweig, H.; Schwab, K. 1,1-Diboration of Isocyanides with [2]Borametalloarenophanes. Organometallics 2010, 29, 934−938. (474) Ishiyama, T.; Momota, S.; Miyaura, N. Platinum(0)-Catalyzed Diboration of Methylenecyclopropanes with Bis(pinacolato)diboron. A Selective Route to 2,4-Bis(boryl)-1-butenes. Synlett 1999, 1790− 1792. (475) Matsuda, T.; Kirikae, H. Palladium-Catalyzed Hydrometalation and Bismetalation of Biphenylene. Organometallics 2011, 30, 3923− 3925. (476) Oshima, K.; Ohmura, T.; Suginome, M. Dearomatizing Conversion of Pyrazines to 1,4-Dihydropyrazine Derivatives via Transition-Metal-Free Diboration, Silaboration, and Hydroboration. Chem. Commun. 2012, 48, 8571−8573. (477) Ohmura, T.; Morimasa, Y.; Suginome, M. Organocatalytic Diboration Involving ″Reductive Addition″ of a Boron-Boron σ-Bond to 4,4 ’-Bipyridine. J. Am. Chem. Soc. 2015, 137, 2852−2855. (478) Lawson, Y. G.; Lesley, M. J. G.; Norman, N. C.; Rice, C. R.; Marder, T. B. Platinum-Catalyzed 1,4-Diboration of α,β-Unsaturated Ketones. Chem. Commun. 1997, 2051−2052. (479) Bell, N. J.; Cox, A. J.; Cameron, N. R.; Evans, J. S. O.; Marder, T. B.; Duin, M. A.; Elsevier, C. J.; Baucherel, X.; Tulloch, A. A. D.; Tooze, R. P. Platinum-Catalyzed 3,4- and 1,4-Diboration of α,βUnsaturated Carbonyl Compounds Using Bis-pinacolatodiboron. Chem. Commun. 2004, 1854−1855. (480) Liu, B.; Gao, M.; Dang, L.; Zhao, H.; Marder, T. B.; Lin, Z. DFT Studies on the Mechanisms of the Platinum-Catalyzed Diboration of Acyclic α,β-Unsaturated Carbonyl Compounds. Organometallics 2012, 31, 3410−3425. (481) Calow, A. D. J.; Whiting, A. Catalytic Methodologies for the βBoration of Conjugated Electron Deficient Alkenes. Org. Biomol. Chem. 2012, 10, 5485−5497. (482) Schiffner, J. A.; Müther, K.; Oestreich, M. Enantioselective Conjugate Borylation. Angew. Chem., Int. Ed. 2010, 49, 1194−1196. (483) Hartmann, E.; Vyas, D. J.; Oestreich, M. Enantioselective Formal Hydration of α,β-Unsaturated Acceptors: Asymmetric BG


Chemical Reviews

Review

Conjugate Addition of Silicon and Boron Nucleophiles. Chem. Commun. 2011, 47, 7917−7932. (484) Liu, Q.; Tian, B.; Tian, P.; Tong, X.; Lin, G.-Q. Recent Progress on Cu-Catalyzed Asymmetric Conjugate Borylation to α,βUnsaturated Compounds. Youji Huaxue 2015, 35, 1−14. (485) Mantilli, L.; Mazet, C. Copper-Catalyzed Asymmetric βBoration of α,β-Unsaturated Carbonyl Derivatives. ChemCatChem 2010, 2, 501−504. (486) Stavber, G.; Casar, Z. Cu-II and Cu-0 Catalyzed Mono Borylation of Unsaturated Hydrocarbons with B2pin2: Entering into the Water. ChemCatChem 2014, 6, 2162−2174. (487) Bonet, A.; Solé, C.; Gulyás, H.; Fernández, E. Boron Conjugate Additions on Electron Deficient Olefins Towards Selective 1,3Difunctionalization. Curr. Org. Chem. 2010, 14, 2531−2548. (488) Ito, H.; Yamanaka, H.; Tateiwa, J. I.; Hosomi, A. Boration of an α,β-Enone Using a Diboron Promoted by a Copper(I)-Phosphine Mixture Catalyst. Tetrahedron Lett. 2000, 41, 6821−6825. (489) Mun, S.; Lee, J.-E.; Yun, J. Copper-Catalyzed β-Boration of α,β-Unsaturated Carbonyl Compounds: Rate Acceleration by Alcohol Additives. Org. Lett. 2006, 8, 4887−4889. (490) Lee, J.-E.; Kwon, J.; Yun, J. Copper-Catalyzed Addition of Diboron Reagents to α,β-Acetylenic Esters: Efficient Synthesis of βBoryl-α,β-Ethylenic Esters. Chem. Commun. 2008, 733−734. (491) Feng, X.; Yun, J. Catalytic Enantioselective Boron Conjugate Addition to Cyclic Carbonyl Compounds: A New Approach to Cyclic β-Hydroxy Carbonyls. Chem. Commun. 2009, 6577−6579. (492) Kim, D.; Park, B.-M.; Yun, J. Highly Efficient Conjugate Reduction of α,β-Unsaturated Nitriles Catalyzed by Copper/ Xanthene-Type Bisphosphine Complexes. Chem. Commun. 2005, 1755−1757. (493) Feng, X.; Yun, J. Conjugate Boration of β,β-Disubstituted Unsaturated Esters: Asymmetric Synthesis of Functionalized Chiral Tertiary Organoboronic Esters. Chem. - Eur. J. 2010, 16, 13609− 13612. (494) Cano, R.; Ramon, D. J.; Yus, M. Impregnated Copper on Magnetite as Recyclable Catalyst for the Addition of Alkoxy Diboron Reagents to C−C Double Bonds. J. Org. Chem. 2010, 75, 3458−3460. (495) Chea, H.; Sim, H.-S.; Yun, J. Ligandless Copper-Catalyzed βBoration of α,β-Unsaturated Compounds in Aqueous Solution. Bull. Korean Chem. Soc. 2010, 31, 551−552. (496) Chen, I. H.; Yin, L.; Itano, W.; Kanai, M.; Shibasaki, M. Catalytic Asymmetric Synthesis of Chiral Tertiary Organoboronic Esters through Conjugate Boration of β-Substituted Cyclic Enones. J. Am. Chem. Soc. 2009, 131, 11664−11665. (497) Sim, H.-S.; Feng, X.; Yun, J. Copper-Catalyzed Enantioselective β-Boration of Acyclic Enones. Chem. - Eur. J. 2009, 15, 1939− 1943. (498) Lee, J.-E.; Yun, J. Catalytic Asymmetric Boration of Acyclic α,β-Unsaturated Esters and Nitriles. Angew. Chem., Int. Ed. 2008, 47, 145−147. (499) Chea, H.; Sim, H.-S.; Yun, J. Copper-Catalyzed Conjugate Addition of Diboron Reagents to α,β-Unsaturated Amides: Highly Reactive Copper-1,2-Bis(diphenylphosphino)benzene Catalyst System. Adv. Synth. Catal. 2009, 351, 855−858. (500) Lee, J. C. H.; McDonald, R.; Hall, D. G. Enantioselective Preparation and Chemoselective Cross-Coupling of 1,1-Diboron Compounds. Nat. Chem. 2011, 3, 894−899. (501) Kitanosono, T.; Kobayashi, S. Asymmetric Boron Conjugate Additions to Enones in Water Catalyzed by Copper(0). Asian J. Org. Chem. 2013, 2, 961−966. (502) Solé, C.; Fernández, E. Catalytic β-Boration/Oxidation of 1Azadienes. Chem. - Asian J. 2009, 4, 1790−1793. (503) Calow, A. D. J.; Solé, C.; Whiting, A.; Fernández, E. Base-Free β-Boration of α,β-Unsaturated Imines Catalysed by Cu2O with Concurrent Enhancement of Asymmetric Induction. ChemCatChem 2013, 5, 2233−2239. (504) Moure, A. L.; Gómez Arráyas, R.; Carretero, J. C. Catalytic Asymmetric Conjugate Boration of α,β-Unsaturated Sulfones. Chem. Commun. 2011, 47, 6701−6703.

(505) Hornillos, V.; Vila, C.; Otten, E.; Feringa, B. L. Catalytic Asymmetric Synthesis of Phosphine Boronates. Angew. Chem., Int. Ed. 2015, 54, 7867−7871. (506) O’Brien, J. M.; Lee, K.-S.; Hoveyda, A. H. Enantioselective Synthesis of Boron-Substituted Quaternary Carbons by NHC-CuCatalyzed Boronate Conjugate Additions to Unsaturated Carboxylic Esters, Ketones, or Thioesters. J. Am. Chem. Soc. 2010, 132, 10630− 10633. (507) Park, J. K.; Lackey, H. H.; Rexford, M. D.; Kovnir, K.; Shatruk, M.; McQuade, D. T. A Chiral 6-Membered N-Heterocyclic Carbene Copper(I) Complex That Induces High Stereoselectivity. Org. Lett. 2010, 12, 5008−5011. (508) Fleming, W. J.; Mueller-Bunz, H.; Lillo, V.; Fernández, E.; Guiry, P. J. Axially Chiral P-N Ligands for the Copper Catalyzed βBorylation of α,β-Unsaturated Esters. Org. Biomol. Chem. 2009, 7, 2520−2524. (509) Bonet, A.; Lillo, V.; Ramírez, J.; Diaz-Requejo, M. M.; Fernández, E. The Selective Catalytic Formation of β-Boryl Aldehydes Through a Base-Free Approach. Org. Biomol. Chem. 2009, 7, 1533− 1535. (510) Lillo, V.; Prieto, A.; Bonet, A.; Díaz-Requejo, M. M.; Ramírez, J.; Perez, P. J.; Fernández, E. Asymmetric β-Boration of α,βUnsaturated Esters with Chiral (NHC)Cu Catalysts. Organometallics 2009, 28, 659−662. (511) Solé, C.; Bonet, A.; de Vries, A. H. M.; de Vries, J. G.; Lefort, L.; Gulyás, H.; Fernández, E. Influence of Phosphoramidites in Copper-Catalyzed Conjugate Borylation Reaction. Organometallics 2012, 31, 7855−7861. (512) Palau-Lluch, G.; Fernández, E. Synthesis of 2-Aryl-1,3Cyclopentanediones through Catalytic Borylation as a Key Step. Asian J. Org. Chem. 2015, 4, 963−968. (513) Hong, B.; Ma, Y.; Zhao, L.; Duan, W.; He, F.; Song, C. Synthesis of Planar Chiral Imidazo[1,5-a]Pyridinium Salts Based on [2.2]Paracyclophane for Asymmetric β-Borylation of Enones. Tetrahedron: Asymmetry 2011, 22, 1055−1062. (514) Zhao, L.; Ma, Y.; He, F.; Duan, W.; Chen, J.; Song, C. Enantioselective β-Boration of Acyclic Enones by a [2.2]Paracyclophane-Based N-Heterocyclic Carbene Copper(I) Catalyst. J. Org. Chem. 2013, 78, 1677−1681. (515) Zhao, L.; Ma, Y.; Duan, W.; He, F.; Chen, J.; Song, C. Asymmetric β-Boration of α,β-Unsaturated N-Acyloxazolidinones by [2.2]Paracyclophane-Based Bifunctional Catalyst. Org. Lett. 2012, 14, 5780−5783. (516) Chen, I. H.; Kanai, M.; Shibasaki, M. Copper(I)-Secondary Diamine Complex-Catalyzed Enantioselective Conjugate Boration of Linear β,β-Disubstituted Enones. Org. Lett. 2010, 12, 4098−4101. (517) Zhang, J.-L.; Chen, L.-A.; Xu, R.-B.; Wang, C.-F.; Ruan, Y.-P.; Wang, A.-E.; Huang, P.-Q. Chiral Imidazo[1,5-a]Tetrahydroquinoline N-Heterocyclic Carbenes and their Copper Complexes for Asymmetric Catalysis. Tetrahedron: Asymmetry 2013, 24, 492−498. (518) Iwai, T.; Akiyama, Y.; Sawamura, M. Synthesis of a Chiral NHeterocyclic Carbene Bearing a m-Terphenyl-Based Phosphate Moiety as an Anionic N-Substituent and Its Application to CopperCatalyzed Enantioselective Boron Conjugate Additions. Tetrahedron: Asymmetry 2013, 24, 729−735. (519) Huang, L. L.; Cao, Y.; Zhao, M. P.; Tang, Z. F.; Sun, Z. H. Asymmetric Borylation of α, β-Unsaturated Esters Catalyzed by Novel Ring Expanded N-Heterocyclic Carbenes Based on Chiral 3,4Dihydro-Quinazolinium Compounds. Org. Biomol. Chem. 2014, 12, 6554−6556. (520) Koppenwallner, M.; Rais, E.; Uzarewicz-Baig, M.; Tabassum, S.; Gilani, M. A.; Wilhelm, R. Synthesis of New Camphor-Based Carbene Ligands and Their Application in a Copper-Catalyzed Michael Addition with B2Pin2. Synthesis 2015, 47, 789−800. (521) Jiang, Q. B.; Guo, T. L.; Yu, Z. K. Copper-Catalyzed Tandem Asymmetric Borylation of β-Chloroalkyl Aryl Ketones and Related Compounds. ChemCatChem 2015, 7, 660−665. BH


Chemical Reviews

Review

Application to the Efficient Asymmetric Synthesis of β-Alcohol Type Sitagliptin Side Chain. Appl. Organomet. Chem. 2013, 27, 159−165. (541) Kitanosono, T.; Xu, P. Y.; Isshiki, S.; Zhu, L.; Kobayashi, S. Cu(II)-Catalyzed Asymmetric Boron Conjugate Addition to α,βUnsaturated Imines in Water. Chem. Commun. 2014, 50, 9336−9339. (542) Zhu, L.; Kitanosono, T.; Xu, P. Y.; Kobayashi, S. A Cu(II)Based Strategy for Catalytic Enantioselective β-Borylation of α, βUnsaturated Acceptors. Chem. Commun. 2015, 51, 11685−11688. (543) Kitanosono, T.; Xu, P.; Kobayashi, S. Heterogeneous and Homogeneous Chiral Cu(II) Catalysis in Water: Enantioselective Boron Conjugate Additions to Dienones and Dienoesters. Chem. Commun. 2013, 49, 8184−8186. (544) Luo, Y. F.; Roy, I. D.; Madec, A. G. E.; Lam, H. W. Enantioselective Synthesis of Allylboronates and Allylic Alcohols by Copper-Catalyzed 1,6-Boration. Angew. Chem., Int. Ed. 2014, 53, 4186−4190. (545) Lillo, V.; Geier, M. J.; Westcott, S. A.; Fernández, E. Ni and Pd Mediate Asymmetric Organoboron Synthesis with Ester Functionality at the β-Position. Org. Biomol. Chem. 2009, 7, 4674−4676. (546) Hirano, K.; Yorimitsu, H.; Oshima, K. Nickel-Catalyzed βBoration of α,β-Unsaturated Esters and Amides with Bis(pinacolato)diboron. Org. Lett. 2007, 9, 5031−5033. (547) Kabalka, G. W.; Das, B. C.; Das, S. Rhodium-Catalyzed 1,4Addition Reactions of Diboron Reagents to Electron Deficient Olefins. Tetrahedron Lett. 2002, 43, 2323−2325. (548) Reilly, S. W.; Akurathi, G.; Box, H. K.; Valle, H. U.; Hollis, T. K.; Webster, C. E. β-Boration of α, β-Unsaturated Carbonyl Compounds in Ethanol and Methanol Catalyzed by CCC-NHC Pincer Rh Complexes. J. Organomet. Chem. 2016, 802, 32−38. (549) Toribatake, K.; Zhou, L.; Tsuruta, A.; Nishiyama, H. Asymmetric β-Boration of α,β-Unsaturated Carbonyl Compounds with Chiral Rh[bis(oxazolinyl)phenyl] Catalysts. Tetrahedron 2013, 69, 3551−3560. (550) Shiomi, T.; Adachi, T.; Toribatake, K.; Zhou, L.; Nishiyama, H. Asymmetric β-Boration of α,β-Unsaturated Carbonyl Compounds Promoted by Chiral Rhodium-Bisoxazolinylphenyl Catalysts. Chem. Commun. 2009, 5987−5989. (551) Bonet, A.; Gulyás, H.; Koshevoy, I. O.; Estevan, F.; Sanau, M.; Ubeda, M. A.; Fernández, E. Tandem β-Boration/Arylation of α,βUnsaturated Carbonyl Compounds by Using a Single Palladium Complex To Catalyze Both Steps. Chem. - Eur. J. 2010, 16, 6382− 6390. (552) Radomkit, S.; Hoveyda, A. H. Enantioselective Synthesis of Boron-Substituted Quaternary Carbon Stereogenic Centers through NHC- Catalyzed Conjugate Additions of (Pinacolato)boron Units to Enones. Angew. Chem., Int. Ed. 2014, 53, 3387−3391. (553) Wu, H.; Garcia, J. M.; Haeffner, F.; Radomkit, S.; Zhugralin, A. R.; Hoveyda, A. H. Mechanism of NHC-Catalyzed Conjugate Additions of Diboron and Borosilane Reagents to α, β-Unsaturated Carbonyl Compounds. J. Am. Chem. Soc. 2015, 137, 10585−10602. (554) Wu, H.; Radomkit, S.; O’Brien, J. M.; Hoveyda, A. H. MetalFree Catalytic Enantioselective C−B Bond Formation: (Pinacolato)boron Conjugate Additions to α,β-Unsaturated Ketones, Esters, Weinreb Amides, and Aldehydes Promoted by Chiral N-Heterocyclic Carbenes. J. Am. Chem. Soc. 2012, 134, 8277−8285. (555) Li, C.-Y.; Kuo, Y.-Y.; Tsai, J.-H.; Yap, G. P. A.; Ong, T.-G. Amine-Linked N-Heterocyclic Carbenes: The Importance of an Pendant Free-Amine Auxiliary in Assisting the Catalytic Reaction. Chem. - Asian J. 2011, 6, 1520−1524. (556) Ibrahem, I.; Breistein, P.; Cordova, A. One-Pot ThreeComponent Highly Selective Synthesis of Homoallylboronates by Using Metal-Free Catalysis. Chem. - Eur. J. 2012, 18, 5175−5179. (557) Wen, K.; Chen, J.; Gao, F.; Bhadury, P. S.; Fan, E.; Sun, Z. Metal Free Catalytic Hydroboration of Multiple Bonds in Methanol Using N-Heterocyclic Carbenes Under Open Atmosphere. Org. Biomol. Chem. 2013, 11, 6350−6356. (558) Wang, L.; Chen, Z.; Ma, M.; Duan, W.; Song, C.; Ma, Y. Synthesis and Application of a Dual Chiral [2.2]Paracyclophane-Based

(522) Ibrahem, I.; Breistein, P.; Cordova, A. One-Pot ThreeComponent Catalytic Enantioselective Synthesis of Homoallylboronates. Angew. Chem., Int. Ed. 2011, 50, 12036−12041. (523) He, Z.-T.; Zhao, Y.-S.; Tian, P.; Wang, C.-C.; Dong, H.-Q.; Lin, G.-Q. Copper-Catalyzed Asymmetric Hydroboration of αDehydroamino Acid Derivatives: Facile Synthesis of Chiral βHydroxy-α-amino Acids. Org. Lett. 2014, 16, 1426−1429. (524) Reis, J. S.; Andrade, L. H. Lipase-Catalyzed Kinetic Resolution of β-Borylated Carboxylic Esters. Tetrahedron: Asymmetry 2012, 23, 1294−1300. (525) Knott, K.; Fishovitz, J.; Thorpe, S. B.; Lee, I.; Santos, W. L. NTerminal Peptidic Boronic Acids Selectively Inhibit Human ClpXP. Org. Biomol. Chem. 2010, 8, 3451−3456. (526) Palau-Lluch, G.; Fernández, E. Building Functionality through Sequential C−B and C−F Bond Formation. Adv. Synth. Catal. 2013, 355, 1464−1470. (527) Solé, C.; Tatla, A.; Mata, J. A.; Whiting, A.; Gulyás, H.; Fernández, E. Catalytic 1,3-Difunctionalization of Organic Backbones through a Highly Stereoselective, One-Pot, Boron ConjugateAddition/Reduction/Oxidation Process. Chem. - Eur. J. 2011, 17, 14248−14257. (528) Solé, C.; Whiting, A.; Gulyás, H.; Fernández, E. Highly Enantio- and Diastereoselective Synthesis of γ-Amino Alcohols from α,β-Unsaturated Imines through a One-Pot β-Boration/Reduction/ Oxidation Sequence. Adv. Synth. Catal. 2011, 353, 376−384. (529) Sailes, H. E.; Watts, J. P.; Whiting, A. Studies on the Asymmetric Reduction of β-Oximino Methyl Ether Boronates: Reagent Control, Double Diastereocontrol and Transmitted Remote Asymmetric Induction. J. Chem. Soc., Perkin Trans. 1 2000, 3362− 3374. (530) Calow, A. D. J.; Batsanov, A. S.; Fernández, E.; Solé, C.; Whiting, A. Novel Transformation of α,β-Unsaturated Aldehydes and Ketones into γ-Amino Alcohols or 1,3-Oxazines via a 4 or 5 Step, OnePot Sequence. Chem. Commun. 2012, 48, 11401−11403. (531) Hartmann, E.; Oestreich, M. Two-Directional Desymmetrization by Double 1,4-Addition of Silicon and Boron Nucleophiles. Org. Lett. 2012, 14, 2406−2409. (532) Calow, A. D. J.; Batsanov, A. S.; Pujol, A.; Solé, C.; Fernández, E.; Whiting, A. A Selective Transformation of Enals into Chiral γAmino Alcohols. Org. Lett. 2013, 15, 4810−4813. (533) Pujol, A.; Calow, A. D. J.; Batsanov, A. S.; Whiting, A. One-Pot Catalytic Asymmetric Borylation of Unsaturated Aldehyde-Derived Imines; Functionalisation to Homoallylic Boronate Carboxylate Ester Derivatives. Org. Biomol. Chem. 2015, 13, 5122−5130. (534) Calow, A. D. J.; Fernández, E.; Whiting, A. Total Synthesis of Fluoxetine and Duloxetine Through an In Situ Imine Formation/ Borylation/Transimination and Reduction Approach. Org. Biomol. Chem. 2014, 12, 6121−6127. (535) Vergote, T.; Nahra, F.; Welle, A.; Luhmer, M.; Wouters, J.; Mager, N.; Riant, O.; Leyssens, T. Unprecedented Copper(I) Bifluoride Complexes: Synthesis, Characterization and Reactivity. Chem. - Eur. J. 2012, 18, 793−798. (536) Molander, G. A.; McKee, S. A. Copper-Catalyzed β-Boration of α,β-Unsaturated Carbonyl Compounds with Tetrahydroxydiborane. Org. Lett. 2011, 13, 4684−4687. (537) Thorpe, S. B.; Guo, X.; Santos, W. L. Regio- and Stereoselective Copper-Catalyzed β-Borylation of Allenoates by a Preactivated Diboron. Chem. Commun. 2011, 47, 424−426. (538) Thorpe, S. B.; Calderone, J. A.; Santos, W. L. Unexpected Copper(II) Catalysis: Catalytic Amine Base Promoted β-Borylation of α,β-Unsaturated Carbonyl Compounds in Water. Org. Lett. 2012, 14, 1918−1921. (539) Kobayashi, S.; Xu, P.; Endo, T.; Ueno, M.; Kitanosono, T. Chiral Copper(II)-Catalyzed Enantioselective Boron Conjugate Additions to α,β-Unsaturated Carbonyl Compounds in Water. Angew. Chem., Int. Ed. 2012, 51, 12763−12766. (540) Stavber, G.; Č asar, Z. Basic CuCO3/Ligand as a New Catalyst for ’On Water’ Borylation of Michael Acceptors, Alkenes and Alkynes: BI


Chemical Reviews

Review

N-Heterocyclic Carbene in Enantioselective β-Boration of Acyclic Enones. Org. Biomol. Chem. 2015, 13, 10691−10698. (559) Bonet, A.; Gulyás, H.; Fernández, E. Metal-Free Catalytic Boration at the β-Position of α,β-Unsaturated Compounds: A Challenging Asymmetric Induction. Angew. Chem., Int. Ed. 2010, 49, 5130−5134. (560) La Cascia, E.; Sanz, X.; Bo, C.; Whiting, A.; Fernández, E. Asymmetric Metal Free β-Boration of α, β-Unsaturated Imines Assisted by (S)-MeBoPhoz. Org. Biomol. Chem. 2015, 13, 1328−1332. (561) Cid, J.; Carbo, J. J.; Fernández, E. A Clear- Cut Example of Selective BpinBdan Activation and Precise Bdan Transfer on Boron Conjugate Addition. Chem. - Eur. J. 2014, 20, 3616−3620. (562) Sugiura, M.; Ishikawa, W.; Kuboyama, Y.; Nakajima, M. Conjugate Addition of Diboron Catalyzed by O-Monoacyltartaric Acids. Synthesis 2015, 47, 2265−2269. (563) Endo, K.; Hirokami, M.; Shibata, T. Synthesis of 1,1Organodiboronates via Rh(I)Cl-Catalyzed Sequential Regioselective Hydroboration of 1-Alkynes. Synlett 2009, 1331−1335. (564) Lee, Y.; Jang, H.; Hoveyda, A. H. Vicinal Diboronates in High Enantiomeric Purity through Tandem Site-Selective NHC-CuCatalyzed Boron-Copper Additions to Terminal Alkynes. J. Am. Chem. Soc. 2009, 131, 18234−18235. (565) Jung, H.-Y.; Yun, J. Copper-Catalyzed Double Borylation of Silylacetylenes: Highly Regio- and Stereoselective Synthesis of synVicinal Diboronates. Org. Lett. 2012, 14, 2606−2609. (566) Semba, K.; Fujihara, T.; Terao, J.; Tsuji, Y. Copper-Catalyzed Borylative Transformations of Non-Polar Carbon-Carbon Unsaturated Compounds Employing Borylcopper as an Active Catalyst Species. Tetrahedron 2015, 71, 2183−2197. (567) Kim, H. R.; Jung, I. G.; Yoo, K.; Jang, K.; Lee, E. S.; Yun, J.; Son, S. U. Bis(imidazoline-2-thione)-Copper(I) Catalyzed Regioselective Boron Addition to Internal Alkynes. Chem. Commun. 2010, 46, 758−760. (568) Kim, H. R.; Yun, J. Highly Regio- and Stereoselective Synthesis of Alkenylboronic Esters by Copper-Catalyzed Boron Additions to Disubstituted Alkynes. Chem. Commun. 2011, 47, 2943−2945. (569) Jung, H.-Y.; Feng, X.; Kim, H.; Yun, J. Copper-Catalyzed Boration of Activated Alkynes. Chiral Boranes via a One-Pot CopperCatalyzed Boration and Reduction Protocol. Tetrahedron 2012, 68, 3444−3449. (570) Moon, J. H.; Jung, H. Y.; Lee, Y. J.; Lee, S. W.; Yun, J.; Lee, J. Y. Origin of Regioselectivity in the Copper-Catalyzed Borylation Reactions of Internal Aryl Alkynes with Bis(pinacolato)diboron. Organometallics 2015, 34, 2151−2159. (571) Pulis, A. P.; Fackler, P.; Aggarwal, V. K. Short Stereoselective Synthesis of the Phytophthora Universal Mating Hormone α1 Using Lithiation/Borylation Reactions. Angew. Chem., Int. Ed. 2014, 53, 4382−4385. (572) Peck, C. L.; Calderone, J. A.; Santos, W. L. Copper(II)Catalyzed-Borylation of Acetylenic Esters in Water. Synthesis 2015, 47, 2242−2248. (573) Jang, H.; Zhugralin, A. R.; Lee, Y.; Hoveyda, A. H. Highly Selective Methods for Synthesis of Internal (α-)Vinylboronates Through Efficient NHC-Cu-Catalyzed Hydroboration of Terminal Alkynes. Utility in Chemical Synthesis and Mechanistic Basis for Selectivity. J. Am. Chem. Soc. 2011, 133, 7859−7871. (574) Moure, A. L.; Gómez Arrayás, R. G.; Cárdenas, D. J.; Alonso, I.; Carretero, J. C. Regiocontrolled CuI-Catalyzed Borylation of Propargylic-Functionalized Internal Alkynes. J. Am. Chem. Soc. 2012, 134, 7219−7222. (575) Levin, E.; Ivry, E.; Diesendruck, C. E.; Lemcoff, N. G. Water in N-Heterocyclic Carbene-Assisted Catalysis. Chem. Rev. 2015, 115, 4607−4692. (576) Moure, A. L.; Mauleón, P.; Arráyas, R. G.; Carretero, J. C. Formal Regiocontrolled Hydroboration of Unbiased Internal Alkynes via Borylation/Allylic Alkylation of Terminal Alkynes. Org. Lett. 2013, 15, 2054−2057. (577) Mitrofanov, A. Y.; Bessmertnykh-Lemeune, A. G.; Beletskaya, I. P. Cu(I) Complexes with Diethoxyphosphoryl-1,10-phenanthrolines

in Catalysis of C−C and C−Heteroatom Bonds Formation. Inorg. Chim. Acta 2015, 431, 297−301. (578) Srinivas, K.; Naga Babu, C.; Prabusankar, G. Linear Cu(I) Chalcogenones: Synthesis and Application in Borylation of Unsymmetrical Alkynes. Dalton Trans. 2015, 44, 15636−15644. (579) Yuan, W.; Ma, S. CuCl-K2CO3-Catalyzed Highly Selective Borylcupration of Internal Alkynes - Ligand Effect. Org. Biomol. Chem. 2012, 10, 7266−7268. (580) Semba, K.; Fujihara, T.; Terao, J.; Tsuji, Y. Copper-Catalyzed Highly Regio- and Stereoselective Directed Hydroboration of Unsymmetrical Internal Alkynes: Controlling Regioselectivity by Choice of Catalytic Species. Chem. - Eur. J. 2012, 18, 4179−4184. (581) Yoshida, H.; Takemoto, Y.; Takaki, K. A Masked Diboron in Cu-Catalysed Borylation Reaction: Highly Regioselective Formal Hydroboration of Alkynes for Synthesis of Branched Alkenylborons. Chem. Commun. 2014, 50, 8299−8302. (582) Yoshida, H.; Takemoto, Y.; Takaki, K. Direct Synthesis of Boron-Protected Alkenyl- and Alkylborons via Copper-Catalyzed Formal Hydroboration of Alkynes and Alkenes. Asian J. Org. Chem. 2014, 3, 1204−1209. (583) Zhao, J.; Niu, Z.; Fu, H.; Li, Y. Ligand-Free Hydroboration of Alkynes Catalyzed by Heterogeneous Copper Powder with High Efficiency. Chem. Commun. 2014, 50, 2058−2060. (584) Zhu, G.; Kong, W.; Feng, H.; Qian, Z. Synthesis of (Z)-1-Thioand (Z)-2-Thio-1-alkenyl Boronates via Copper-Catalyzed Regiodivergent Hydroboration of Thioacetylenes: An Experimental and Theoretical Study. J. Org. Chem. 2014, 79, 1786−1795. (585) Chae, Y. M.; Bae, J. S.; Moon, J. H.; Lee, J. Y.; Yun, J. CopperCatalyzed Monoborylation of Silylalkynes; Regio- and Stereoselective Synthesis of (Z)-β-(Borylvinyl) silanes. Adv. Synth. Catal. 2014, 356, 843−849. (586) Kubota, K.; Yamamoto, E.; Ito, H. Regio- and Enantioselective Monoborylation of Alkenylsilanes Catalyzed by an Electron-Donating Chiral Phosphine-Copper(I) Complex. Adv. Synth. Catal. 2013, 355, 3527−3531. (587) Kim, Y. E.; Li, D. X.; Yun, J. Regioselective Synthesis of Highly Functionalized Alkenylboronates by Cu-Catalyzed Borylation of Propargylic Silylalkynes. Dalton Trans. 2015, 44, 12091−12093. (588) He, G. K.; Chen, S.; Wang, Q.; Huang, H.; Zhang, Q. J.; Zhang, D. M.; Zhang, R.; Zhu, H. J. Studies on Copper(I)-Catalyzed Highly Regio- and Stereo-Selective Hydroboration of Alkynamides. Org. Biomol. Chem. 2014, 12, 5945−5953. (589) Bai, Y. H.; Zhang, F.; Shen, J. J.; Luo, F.; Zhu, G. G. CopperCatalyzed-Selective Hydroborylation of Ynamides: A Facile Access to (E)-Alkenylamide Boronates. Asian J. Org. Chem. 2015, 4, 626−629. (590) Park, J. K.; Ondrusek, B. A.; McQuade, D. T. Regioselective Catalytic Hydroboration of Propargylic Species Using Cu(I)-NHC Complexes. Org. Lett. 2012, 14, 4790−4793. (591) Lazreg, F.; Nahra, F.; Cazin, C. S. J. Copper-NHC Complexes in Catalysis. Coord. Chem. Rev. 2015, 293-294, 48−79. (592) Feng, Q.; Yang, K.; Song, Q. Highly Selective CopperCatalyzed Trifunctionalization of Alkynyl Carboxylic Acids: An Efficient Route to Bis-Deuterated β-Borylated α,β-Styrene. Chem. Commun. 2015, 51, 15394−15397. (593) Li, D.; Kim, Y. E.; Yun, J. Highly Regio- and Stereoselective Synthesis of Boron-Substituted Enynes via Copper-Catalyzed Borylation of Conjugated Diynes. Org. Lett. 2015, 17, 860−863. (594) Bidal, Y. D.; Lazreg, F.; Cazin, C. S. J. Copper-Catalyzed Regioselective Formation of Tri- and Tetrasubstituted Vinylboronates in Air. ACS Catal. 2014, 4, 1564−1569. (595) Ojha, D. P.; Prabhu, K. R. Pd-Catalyzed Hydroborylation of Alkynes: A Ligand Controlled Regioselectivity Switch for the Synthesis of α- or β-Vinylboronates. Org. Lett. 2016, 18, 432−435. (596) Yoshida, H.; Kageyuki, I.; Takaki, K. Silver-Catalyzed Highly Regioselective Formal Hydroboration of Alkynes. Org. Lett. 2014, 16, 3512−3515. (597) Fang, G.; Bi, X. Silver-Catalysed Reactions of Alkynes: Recent Advances. Chem. Soc. Rev. 2015, 44, 8124−8173. BJ


Chemical Reviews

Review

Enantioenriched Cyclic Homoallyl- and Allylboronates. J. Am. Chem. Soc. 2010, 132, 1226−1227. (618) Sasaki, Y.; Horita, Y.; Zhong, C.; Sawamura, M.; Ito, H. Copper(I)-Catalyzed Regioselective Monoborylation of 1,3-Enynes with an Internal Triple Bond: Selective Synthesis of 1,3-Dienylboronates and 3-Alkynylboronates. Angew. Chem., Int. Ed. 2011, 50, 2778−2782. (619) Kubota, K.; Hayama, K.; Iwamoto, H.; Ito, H. Enantioselective Borylative Dearomatization of Indoles through Copper(I) Catalysis. Angew. Chem., Int. Ed. 2015, 54, 8809−8813. (620) Yuan, W.; Ma, S. Ligand Controlled Highly Selective CopperCatalyzed Borylcuprations of Allenes with Bis(pinacolato)diboron. Adv. Synth. Catal. 2012, 354, 1867−1872. (621) Meng, F.; Jung, B.; Haeffner, F.; Hoveyda, A. H. NHC-CuCatalyzed Protoboration of Monosubstituted Allenes. Ligand-Controlled Site Selectivity, Application to Synthesis and Mechanism. Org. Lett. 2013, 15, 1414−1417. (622) Jang, H.; Jung, B.; Hoveyda, A. H. Catalytic Enantioselective Protoboration of Disubstituted Allenes. Access to Alkenylboron Compounds in High Enantiomeric Purity. Org. Lett. 2014, 16, 4658−4661. (623) Semba, K.; Shinomiya, M.; Fujihara, T.; Terao, J.; Tsuji, Y. Highly Selective Copper-Catalyzed Hydroboration of Allenes and 1,3Dienes. Chem. - Eur. J. 2013, 19, 7125−7132. (624) Semba, K.; Fujihara, T.; Terao, J.; Tsuji, Y. Copper-Catalyzed Borylation of α-Alkoxy Allenes with Bis(pinacolato)diboron: Efficient Synthesis of 2-Boryl 1,3-Butadienes. Angew. Chem., Int. Ed. 2013, 52, 12400−12403. (625) Yuan, W.; Zhang, X.; Yu, Y.; Ma, S. Amide-Controlled Highly Selective Catalytic Borylcupration of Allenes. Chem. - Eur. J. 2013, 19, 7193−7202. (626) Yuan, W.; Song, L.; Ma, S. Copper-Catalyzed Borylcupration of Allenylsilanes. Angew. Chem., Int. Ed. 2016, 55, 3140−3143. (627) Zhu, C.; Yang, B.; Qiu, Y.; Baeckvall, J. E. Olefin-Directed Palladium-Catalyzed Regio- and Stereoselective Hydroboration of Allenes. Chem. - Eur. J. 2016, 22, 2939−2943. (628) Molander, G. A.; Wisniewski, S. R. Stereospecific CrossCoupling of Secondary Organotrifluoroborates: Potassium 1(Benzyloxy)alkyltrifluoroborates. J. Am. Chem. Soc. 2012, 134, 16856−16868. (629) Kubota, K.; Yamamoto, E.; Ito, H. Copper(I)-Catalyzed Enantioselective Nucleophilic Borylation of Aldehydes: An Efficient Route to Enantiomerically Enriched α-Alkoxyorganoboronate Esters. J. Am. Chem. Soc. 2015, 137, 420−424. (630) Ananikov, V. P.; Szilagyi, R.; Morokuma, K.; Musaev, D. G. Can Steric Effects Induce the Mechanism Switch in the RhodiumCatalyzed Imine Boration Reaction? A Density Functional and ONIOM Study. Organometallics 2005, 24, 1938−1946. (631) Beenen, M. A.; An, C.; Ellman, J. A. Asymmetric CopperCatalyzed Synthesis of α-Amino Boronate Esters from N-tertButanesulfinyl Aldimines. J. Am. Chem. Soc. 2008, 130, 6910−6911. (632) Adams, J.; Behnke, M.; Chen, S.; Cruickshank, A. A.; Dick, L. R.; Grenier, L.; Klunder, J. M.; Ma, Y.-T.; Plamondon, L.; Stein, R. L. Potent and Selective Inhibitors of the Proteasome: Dipeptidyl Boronic Acids. Bioorg. Med. Chem. Lett. 1998, 8, 333−338. (633) Paramore, A.; Frantz, S. Bortezomib. Nat. Rev. Drug Discovery 2003, 2, 611−612. (634) Wen, K.; Wang, H.; Chen, J.; Zhang, H.; Cui, X.; Wei, C.; Fan, E.; Sun, Z. Improving Carbene−Copper-Catalyzed Asymmetric Synthesis of α-Aminoboronic Esters Using Benzimidazole-Based Precursors. J. Org. Chem. 2013, 78, 3405−3409. (635) Buesking, A. W.; Bacauanu, V.; Cai, I.; Ellman, J. A. Asymmetric Synthesis of Protected α-Amino Boronic Acid Derivatives with an Air- and Moisture-Stable Cu(II) Catalyst. J. Org. Chem. 2014, 79, 3671−3677. (636) Zhang, S.-S.; Zhao, Y.-S.; Tian, P.; Lin, G.-Q. Chiral NHC/Cu (I)-Catalyzed Asymmetric Hydroboration of Aldimines: Enantioselective Synthesis of α-Amido Boronic Esters. Synlett 2013, 24, 437− 442.

(598) Rawat, V. S.; Sreedhar, B. Iron-Catalyzed Borylation Reactions of Alkynes: An Efficient Synthesis of E-Vinyl Boronates. Synlett 2014, 25, 1132−1136. (599) Nagashima, Y.; Takita, R.; Yoshida, K.; Hirano, K.; Uchiyama, M. Design, Generation, and Synthetic Application of Borylzincate: Borylation of Aryl Halides and Borylzincation of Benzynes/Terminal Alkyne. J. Am. Chem. Soc. 2013, 135, 18730−18733. (600) Yang, K.; Song, Q. Transition-Metal-Free Regioselective Synthesis of Alkylboronates from Arylacetylenes and Vinyl Arenes. Green Chem. 2016, 18, 932−936. (601) Brown, H. C.; Rao, B. C. S. Hydroboration of Olefins - a Remarkably Fast Room-Temperature Addition of Diborane to Olefins. J. Org. Chem. 1957, 22, 1136−1137. (602) Laitar, D. S.; Tsui, E. Y.; Sadighi, J. P. Copper(I) β-Boroalkyls from Alkene Insertion: Isolation and Rearrangement. Organometallics 2006, 25, 2405−2408. (603) Lee, Y.; Hoveyda, A. H. Efficient Boron-Copper Additions to Aryl-Substituted Alkenes Promoted by NHC-Based Catalysts. Enantioselective Cu-Catalyzed Hydroboration Reactions. J. Am. Chem. Soc. 2009, 131, 3160−3161. (604) Guiry, P. J. Expanding the Substrate Scope for Metal-Catalyzed Asymmetric Carbon-Boron Bond Formation. ChemCatChem 2009, 1, 233−235. (605) Corberan, R.; Mszar, N. W.; Hoveyda, A. H. NHC-CuCatalyzed Enantioselective Hydroboration of Acyclic and Exocyclic 1,1-Disubstituted Aryl Alkenes. Angew. Chem., Int. Ed. 2011, 50, 7079− 7082. (606) Meng, F. K.; Jang, H. J.; Hoveyda, A. H. Exceptionally E- and β-Selective NHCCu-Catalyzed Proto-Silyl Additions to Terminal Alkynes and Site- and Enantioselective Proto-Boryl Additions to the Resulting Vinylsilanes: Synthesis of Enantiomerically Enriched Vicinal and Geminal Borosilanes. Chem. - Eur. J. 2013, 19, 3204−3214. (607) Iwasaki, H.; Teshima, Y.; Yamada, Y.; Ishikawa, R.; Koga, Y.; Matsubara, K. Bimetallic Cu(I) Complex with a Pyridine-Bridged Bis(1,2,3-triazole-5-ylidene) Ligand. Dalton Trans. 2016, 45, 5713− 5719. (608) Hong, S. B.; Liu, M. Y.; Zhang, W.; Zeng, Q.; Deng, W. Copper-Catalyzed Hydroboration of Arylalkenes at Room Temperature. Tetrahedron Lett. 2015, 56, 2297−2302. (609) Wen, Y. M.; Xie, J. Y.; Deng, C. M.; Li, C. D. Selective Synthesis of Alkylboronates by Copper(I)-Catalyzed Borylation of Allyl or Vinyl Arenes. J. Org. Chem. 2015, 80, 4142−4147. (610) Liu, Y.; Zhou, Y. H.; Wang, H.; Qu, J. P. FeCl2-Catalyzed Hydroboration of Aryl Alkenes with Bis(pinacolato) diboron. RSC Adv. 2015, 5, 73705−73713. (611) Zhao, W. X.; Montgomery, J. Functionalization of Styrenes by Copper-Catalyzed Borylation/ortho-Cyanation and Silver-Catalyzed Annulation Processes. Angew. Chem., Int. Ed. 2015, 54, 12683−12686. (612) Parra, A.; Amenos, L.; Guisan-Ceinos, M.; López, A.; García Ruano, J. L.; Tortosa, M. Copper-Catalyzed Diastereo- and Enantioselective Desymmetrization of Cyclopropenes: Synthesis of Cyclopropylboronates. J. Am. Chem. Soc. 2014, 136, 15833−15836. (613) Parra, A.; López, A.; Diaz-Tendero, S.; Amenos, L.; Ruano, J. L. G.; Tortosa, M. Insight into the Copper-Catalyzed Borylation of Strained Alkenes. Synlett 2015, 26, 494−500. (614) Lee, H.; Lee, B. Y.; Yun, J. Copper(I)-Taniaphos Catalyzed Enantiodivergent Hydroboration of Bicyclic Alkenes. Org. Lett. 2015, 17, 764−766. (615) Lou, Y. Z.; Cao, P.; Jia, T.; Zhang, Y. L.; Wang, M.; Liao, J. Copper-Catalyzed Enantioselective 1,6-Boration of para-Quinone Methides and Efficient Transformation of gem-Diarylmethine Boronates to Triarylmethanes. Angew. Chem., Int. Ed. 2015, 54, 12134−12138. (616) Jarava-Barrera, C.; Parra, A.; López, A.; Cruz-Acosta, F.; Collado-Sanz, D.; Cárdenas, D. J.; Tortosa, M. Copper-Catalyzed Borylative Aromatization of p-Quinone Methides: Enantioselective Synthesis of Dibenzylic Boronates. ACS Catal. 2016, 6, 442−446. (617) Sasaki, Y.; Zhong, C.; Sawamura, M.; Ito, H. Copper(I)Catalyzed Asymmetric Monoborylation of 1,3-Dienes: Synthesis of BK


Chemical Reviews

Review

(637) Wang, D.; Cao, P.; Wang, B.; Jia, T.; Lou, Y. Z.; Wang, M.; Liao, J. Copper(I)-Catalyzed Asymmetric Pinacolboryl Addition of NBoc-imines Using a Chiral Sulfoxide-Phosphine Ligand. Org. Lett. 2015, 17, 2420−2423. (638) Xie, J. B.; Luo, J.; Winn, T. R.; Cordes, D. B.; Li, G. G. GroupAssisted Purification (GAP) Chemistry for the Synthesis of Velcade via Asymmetric Borylation of N-Phosphinylimines. Beilstein J. Org. Chem. 2014, 10, 746−751. (639) Hu, N. F.; Zhao, G. Q.; Zhang, Y. Y.; Liu, X. Q.; Li, G. Y.; Tang, W. J. Synthesis of Chiral α-Amino Tertiary Boronic Esters by Enantioselective Hydroboration of α-Arylenamides. J. Am. Chem. Soc. 2015, 137, 6746−6749. (640) Shimizu, M.; Fujimoto, T.; Minezaki, H.; Hata, T.; Hiyama, T. New, General, and Stereoselective Synthesis of CF3-Containing Triand Tetrasubstituted Oxiranes and Tetrasubstituted Alkenes. J. Am. Chem. Soc. 2001, 123, 6947−6948. (641) Tortosa, M. Synthesis of syn and anti 1,4-Diols by CopperCatalyzed Boration of Allylic Epoxides. Angew. Chem., Int. Ed. 2011, 50, 3950−3953. (642) Sebelius, S.; Olsson, V. J.; Szabó, K. J. Palladium Pincer Complex Catalyzed Substitution of Vinyl Cyclopropanes, Vinyl Aziridines, and Allyl Acetates with Tetrahydroxydiboron. An Efficient Route to Functionalized Allylboronic Acids and Potassium Trifluoro(allyl)borates. J. Am. Chem. Soc. 2005, 127, 10478−10479. (643) Zhao, J.; Szabó, K. J. Catalytic Borylative Opening of Propargyl Cyclopropane, Epoxide, Aziridine, and Oxetane Substrates: Ligand Controlled Synthesis of Allenyl Boronates and Alkenyl Diboronates. Angew. Chem., Int. Ed. 2016, 55, 1502−1506. (644) Sumida, Y.; Yorimitsu, H.; Oshima, K. Nickel-Catalyzed Borylative Ring-Opening Reaction of Vinylcyclopropanes with Bis(pinacolato)diboron Yielding Allylic Boronates. Org. Lett. 2008, 10, 4677−4679. (645) Sumida, Y.; Yorimitsu, H.; Oshima, K. Nickel-Catalyzed Borylation of Aryl Cyclopropyl Ketones with Bis(pinacolato)diboron to Synthesize 4-Oxoalkylboronates. J. Org. Chem. 2009, 74, 3196− 3198. (646) Crotti, S.; Bertolini, F.; Macchia, F.; Pineschi, M. NickelCatalyzed Borylative Ring Opening of Vinyl Epoxides and Aziridines. Org. Lett. 2009, 11, 3762−3765. (647) Pineschi, M. Advances in the Ring Opening of Small-Ring Heterocycles with Organoboron Derivatives. Synlett 2014, 25, 1817− 1826. (648) Marco-Martínez, J.; López-Carrillo, V.; Buñuel, E.; Simancas, R.; Cárdenas, D. J. Pd-Catalyzed Borylative Cyclization of 1,6-Enynes. J. Am. Chem. Soc. 2007, 129, 1874−1875. (649) Tsukamoto, H.; Matsumoto, T.; Kondo, Y. MicrowaveAssisted Palladium(0)-Catalyzed Alkylative Cyclization of Allenyl Aldehydes Leading to 3-Substituted 3-Cycloalken-1-ols. J. Am. Chem. Soc. 2008, 130, 388−389. (650) Miura, T.; Takahashi, Y.; Murakami, M. Rhodium-Catalyzed Borylative Cyclization of 2-Alkynylaryl Isocyanates with Bis(pinacolato)diboron. Org. Lett. 2008, 10, 1743−1745. (651) Tsukamoto, H.; Kondo, Y. Palladium(0)-Catalyzed Alkynyl and Allenyl Iminium Ion Cyclizations leading to 1,4-Disubstituted 1,2,3,6-Tetrahydropyridines. Angew. Chem., Int. Ed. 2008, 47, 4851− 4854. (652) Huang, J.; Macdonald, S. J. F.; Harrity, J. P. A. A Borylative Cyclisation Towards Indole Boronic Esters. Chem. Commun. 2009, 46, 8770−8772. (653) Camelio, A. M.; Barton, T.; Guo, F.; Shaw, T.; Siegel, D. Hydroxyl-Directed Cyclizations of 1,6-Enynes. Org. Lett. 2011, 13, 1517−1519. (654) Martos-Redruejo, A.; López-Durán, R.; Buñuel, E.; Cárdenas, D. J. Ligand-Controlled Divergent Formation of Alkenyl- or Allylboronates Catalyzed by Pd, and Synthetic Applications. Chem. Commun. 2014, 50, 10094−10097. (655) Marco-Martínez, J.; Buñuel, E.; López-Durán, R.; Cárdenas, D. J. Pd-Catalyzed Borylative Polycyclization of Enediynes to Alkylboronates. Chem. - Eur. J. 2011, 17, 2734−2741.

(656) Marco-Martínez, J.; Buñ uel, E.; Munoz-Rodriguez, R.; Cárdenas, D. J. Pd-Catalyzed Borylative Polycyclization of Enediynes to Allylboronates. Org. Lett. 2008, 10, 3619−3621. (657) Deng, Y.; Bartholomeyzik, T.; Persson, A. K. A.; Sun, J.; Bäckvall, J.-E. Palladium-Catalyzed Oxidative Arylating Carbocyclization of Allenynes. Angew. Chem., Int. Ed. 2012, 51, 2703−2707. (658) Deng, Y.; Bartholomeyzik, T.; Bäckvall, J.-E. Control of Selectivity in Palladium-Catalyzed Oxidative Carbocyclization/Borylation of Allenynes. Angew. Chem., Int. Ed. 2013, 52, 6283−6287. (659) Persson, A. K. A.; Jiang, T.; Johnson, M. T.; Bäckvall, J.-E. Palladium-Catalyzed Oxidative Borylative Carbocyclization of Enallenes. Angew. Chem., Int. Ed. 2011, 50, 6155−6159. (660) Pardo-Rodríguez, V.; Marco-Martínez, J.; Buñuel, E.; Cárdenas, D. J. Pd-Catalyzed Borylative Cyclization of Allenynes and Enallenes. Org. Lett. 2009, 11, 4548−4551. (661) Jiang, T.; Bartholomeyzik, T.; Mazuela, J.; Willersinn, J.; Bäckvall, J.-E. Palladium(II)/Brønsted Acid-Catalyzed Enantioselective Oxidative Carbocyclization−Borylation of Enallenes. Angew. Chem., Int. Ed. 2015, 54, 6024−6027. (662) Tobisu, M.; Fujihara, H.; Koh, K.; Chatani, N. Synthesis of 2Boryl- and Silylindoles by Copper-Catalyzed Borylative and Silylative Cyclization of 2-Alkenylaryl Isocyanides. J. Org. Chem. 2010, 75, 4841−4847. (663) Pardo-Rodríguez, V.; Buñuel, E.; Collado-Sanz, D.; Cárdenas, D. J. Pd-Catalyzed Borylative Cyclisation of 1,7-Enynes. Chem. Commun. 2012, 48, 10517−10519. (664) Burns, A. R.; Solana González, G.; Lam, H. W. Enantioselective Copper(I)-Catalyzed Borylative Aldol Cyclizations of Enone Diones. Angew. Chem., Int. Ed. 2012, 51, 10827−10831. (665) Liu, P.; Fukui, Y.; Tian, P.; He, Z.-T.; Sun, C.-Y.; Wu, N.-Y.; Lin, G.-Q. Cu-Catalyzed Asymmetric Borylative Cyclization of Cyclohexadienone-Containing 1,6-Enynes. J. Am. Chem. Soc. 2013, 135, 11700−11703. (666) López-Durán, R.; Martos-Redruejo, A.; Buñuel, E.; PardoRodríguez, V.; Cárdenas, D. J. Preparation of Allylboronates by PdCatalysed Borylative Cyclisation of Dienynes. Chem. Commun. 2013, 49, 10691−10693. (667) Cho, H. Y.; Yu, Z.; Morken, J. P. Stereoselective Borylative Ketone-Diene Coupling. Org. Lett. 2011, 13, 5267−5269. (668) Ballard, C. E.; Morken, J. P. Platinum-Catalyzed Tandem Diboration/Intramolecular Allylboration: Diastereoselective Access to Cyclohexanes Bearing 1,3-Diols. Synthesis 2004, 1321−1324. (669) Mannathan, S.; Jeganmohan, M.; Cheng, C.-H. NickelCatalyzed Borylative Coupling of Alkynes, Enones, and Bis(pinacolato)diboron as a Route to Substituted Alkenyl Boronates. Angew. Chem., Int. Ed. 2009, 48, 2192−2195. (670) Welle, A.; Cirriez, V.; Riant, O. Copper Catalyzed Tandem Conjugated Borylation-Aldol Reaction. Tetrahedron 2012, 68, 3435− 3443. (671) Yamamoto, E.; Kojima, R.; Kubota, K.; Ito, H. Copper(I)Catalyzed Diastereoselective Borylative Exo-Cyclization of Alkenyl Aryl Ketones. Synlett 2016, 27, 272−276. (672) Zhang, L.; Cheng, J.; Carry, B.; Hou, Z. Catalytic Boracarboxylation of Alkynes with Diborane and Carbon Dioxide by an N-Heterocyclic Carbene Copper Catalyst. J. Am. Chem. Soc. 2012, 134, 14314−14317. (673) Takemoto, Y.; Yoshida, H.; Takaki, K. Copper-Catalyzed Three-Component Borylstannylation of Alkynes. Chem. - Eur. J. 2012, 18, 14841−14844. (674) Yoshida, H.; Takemoto, Y.; Takaki, K. Borylstannylation of Alkynes with Inverse Regioselectivity: Copper-Catalyzed ThreeComponent Coupling Using a Masked Diboron. Chem. Commun. 2015, 51, 6297−6300. (675) Takemoto, Y.; Yoshida, H.; Takaki, K. Facile Access to vicBorylstannylalkanes via Copper-Catalyzed Three-Component Borylstannylation of Alkenes. Synthesis 2014, 46, 3024−3032. (676) Jia, T.; Cao, P.; Wang, D.; Lou, Y. Z.; Liao, J. CopperCatalyzed Asymmetric Three-Component Borylstannation: EnantioBL


Chemical Reviews

Review

selective Formation of C−Sn Bond. Chem. - Eur. J. 2015, 21, 4918− 4922. (677) Matsuda, N.; Hirano, K.; Satoh, T.; Miura, M. Regioselective and Stereospecific Copper-Catalyzed Aminoboration of Styrenes with Bis(pinacolato)diboron and O-benzoyl-N,N-dialkylhydroxylamines. J. Am. Chem. Soc. 2013, 135, 4934−4937. (678) Sakae, R.; Matsuda, N.; Hirano, K.; Satoh, T.; Miura, M. Highly Stereoselective Synthesis of (Borylmethyl)cyclopropylamines by Copper-Catalyzed Aminoboration of Methylenecyclopropanes. Org. Lett. 2014, 16, 1228−1231. (679) Sakae, R.; Hirano, K.; Satoh, T.; Miura, M. Copper-Catalyzed Stereoselective Aminoboration of Bicyclic Alkenes. Angew. Chem., Int. Ed. 2015, 54, 613−617. (680) Sakae, R.; Hirano, K.; Miura, M. Ligand-Controlled Regiodivergent Cu-Catalyzed Aminoboration of Unactivated Terminal Alkenes. J. Am. Chem. Soc. 2015, 137, 6460−6463. (681) Meng, F. K.; Jang, H.; Jung, B.; Hoveyda, A. H. Cu-Catalyzed Chemoselective Preparation of 2-(Pinacolato)boron-Substituted Allylcopper Complexes and their In Situ Site-, Diastereo-, and Enantioselective Additions to Aldehydes and Ketones. Angew. Chem., Int. Ed. 2013, 52, 5046−5051. (682) Meng, F. K.; Haeffner, F.; Hoveyda, A. H. Diastereo- and Enantioselective Reactions of Bis(pinacolato)diboron, 1,3-Enynes, and Aldehydes Catalyzed by an Easily Accessible Bisphosphine-Cu Complex. J. Am. Chem. Soc. 2014, 136, 11304−11307. (683) Rae, J.; Yeung, K.; McDouall, J. J. W.; Procter, D. J. CopperCatalyzed Borylative Cross-Coupling of Allenes and Imines: Selective Three-Component Assembly of Branched Homoallyl Amines. Angew. Chem., Int. Ed. 2016, 55, 1102−1107. (684) Smith, J. J.; Best, D.; Lam, H. W. Copper-Catalyzed Borylative Coupling of Vinylazaarenes and N-Boc Imines. Chem. Commun. 2016, 52, 3770−3772. (685) Yang, F.-Y.; Wu, M.-Y.; Cheng, C.-H. Highly Regio- and Stereoselective Acylboration of Allenes Catalyzed by Palladium Complexes: An Efficient Route to a New Class of 2-Acylallylboronates. J. Am. Chem. Soc. 2000, 122, 7122−7123. (686) Yang, F.-Y.; Shanmugasundaram, M.; Chuang, S.-Y.; Ku, P.-J.; Wu, M.-Y.; Cheng, C.-H. Highly Regio- and Stereoselective Acylboration, Acylsilation, and Acylstannation of Allenes Catalyzed by Phosphine-Free Palladium Complexes: An Efficient Route to a New Class of 2-Acylallylmetal Reagents. J. Am. Chem. Soc. 2003, 125, 12576−12583. (687) Söderberg, B. C. G. Transition Metals in Organic Synthesis: Highlights for the Year 2000. Coord. Chem. Rev. 2003, 241, 147−247. (688) Yoshida, H.; Kageyuki, I.; Takaki, K. Copper-Catalyzed ThreeComponent Carboboration of Alkynes and Alkenes. Org. Lett. 2013, 15, 952−955. (689) Alfaro, R.; Parra, A.; Aleman, J.; Garcia Ruano, R. J. L.; Tortosa, M. Copper(I)-Catalyzed Formal Carboboration of Alkynes: Synthesis of Tri- and Tetrasubstituted Vinylboronates. J. Am. Chem. Soc. 2012, 134, 15165−15168. (690) Kageyuki, I.; Yoshida, H.; Takaki, K. Three-Component Carboboration of Alkenes under Copper Catalysis. Synthesis 2014, 46, 1924−1932. (691) Zhou, Y. Q.; You, W.; Smith, K. B.; Brown, M. K. CopperCatalyzed Cross-Coupling of Boronic Esters with Aryl Iodides and Application to the Carboboration of Alkynes and Allenes. Angew. Chem., Int. Ed. 2014, 53, 3475−3479. (692) Su, W.; Gong, T. J.; Lu, X.; Xu, M. Y.; Yu, C. G.; Xu, Z. Y.; Yu, H. Z.; Xiao, B.; Fu, Y. Ligand-Controlled Regiodivergent CopperCatalyzed Alkylboration of Alkenes. Angew. Chem., Int. Ed. 2015, 54, 12957−12961. (693) Semba, K.; Nakao, Y. Arylboration of Alkenes by Cooperative Palladium/Copper Catalysis. J. Am. Chem. Soc. 2014, 136, 7567−7570. (694) Smith, K. B.; Logan, K. M.; You, W.; Brown, M. K. Alkene Carboboration Enabled by Synergistic Catalysis. Chem. - Eur. J. 2014, 20, 12032−12036.

(695) Logan, K. M.; Smith, K. B.; Brown, M. K. Copper/Palladium Synergistic Catalysis for the syn- and anti-Selective Carboboration of Alkenes. Angew. Chem., Int. Ed. 2015, 54, 5228−5231. (696) Jia, T.; Cao, P.; Wang, B.; Lou, Y. Z.; Yin, X. M.; Wang, M.; Liao, J. A Cu/Pd Cooperative Catalysis for Enantioselective Allylboration of Alkenes. J. Am. Chem. Soc. 2015, 137, 13760−13763. (697) Yang, K.; Song, Q. Palladium-Catalyzed Arylboration of Bicyclic Alkenes. J. Org. Chem. 2016, 81, 1000−1005. (698) Kubota, K.; Yamamoto, E.; Ito, H. Copper(I)-Catalyzed Borylative exo-Cyclization of Alkenyl Halides Containing Unactivated Double Bond. J. Am. Chem. Soc. 2013, 135, 2635−2640. (699) Zhong, C.; Kunii, S.; Kosaka, Y.; Sawamura, M.; Ito, H. Enantioselective Synthesis of trans-Aryl- and -Heteroaryl-Substituted Cyclopropylboronates by Copper(I)-Catalyzed Reactions of Allylic Phosphates with a Diboron Derivative. J. Am. Chem. Soc. 2010, 132, 11440−11442. (700) Semba, K.; Bessho, N.; Fujihara, T.; Terao, J.; Tsuji, Y. Copper-Catalyzed Borylative Allyl-Allyl Coupling Reaction. Angew. Chem., Int. Ed. 2014, 53, 9007−9011. (701) Meng, F. K.; McGrath, K. P.; Hoveyda, A. H. Multifunctional Organoboron Compounds for Scalable Natural Product Synthesis. Nature 2014, 513, 367−374. (702) Bin, H. Y.; Wei, X.; Zi, J.; Zuo, Y. J.; Wang, T. C.; Zhong, C. M. Substrate-Controlled Regio- and Stereoselective Synthesis of BoronSubstituted 1,4-Dienes via Copper-Catalyzed Boryl-Allylation of Alkynes with Allyl Phosphates and Bis(pinacolato)diboron. ACS Catal. 2015, 5, 6670−6679. (703) Kubota, K.; Iwamoto, H.; Yamamoto, E.; Ito, H. SiliconTethered Strategy for Copper(I)-Catalyzed Stereo- and Regioselective Alkylboration of Alkynes. Org. Lett. 2015, 17, 620−623. (704) Vachhani, D. D.; Butani, H. H.; Sharma, N.; Bhoya, U. C.; Shah, A. K.; Van der Eycken, E. V. Domino Heck/Borylation Sequence Towards Indolinone-3-methyl Boronic Esters: Trapping of the σ-Alkylpalladium Intermediate with Boron. Chem. Commun. 2015, 51, 14862−14865. (705) Itoh, T.; Matsueda, T.; Shimizu, Y.; Kanai, M. CopperCatalyzed Oxyboration of Unactivated Alkenes. Chem. - Eur. J. 2015, 21, 15955−15959. (706) Yang, Y. Regio- and Stereospecific 1,3-Allyl Group Transfer Triggered by a Copper-Catalyzed Borylation/ortho-Cyanation Cascade. Angew. Chem., Int. Ed. 2016, 55, 345−349. (707) Shi, H.; Babinski, D. J.; Ritter, T. Modular C-H Functionalization Cascade of Aryl Iodides. J. Am. Chem. Soc. 2015, 137, 3775−3778. (708) Ishiyama, T.; Ahiko, T.-A.; Miyaura, N. A Synthesis of Allyboronates via the Palladium(0)-Catalyzed Cross-Coupling Reaction of Bis(pinacolato)diboron with Allylic Acetates. Tetrahedron Lett. 1996, 37, 6889−6892. (709) Sebelius, S.; Wallner, O. A.; Szabó, K. J. Palladium-Catalyzed Coupling of Allyl Acetates with Aldehyde and Imine Electrophiles in the Presence of Bis(pinacolato)diboron. Org. Lett. 2003, 5, 3065− 3068. (710) Sebelius, S.; Szabó, K. J. Allylation of Aldehyde and Imine Substrates with In Situ Generated Allylboronates - a Simple Route to Enantioenriched Homoallyl Alcohols. Eur. J. Org. Chem. 2005, 2539− 2547. (711) Zhang, P.; Roundtree, I. A.; Morken, J. P. Ni- and PdCatalyzed Synthesis of Substituted and Functionalized Allylic Boronates. Org. Lett. 2012, 14, 1416−1419. (712) Ahiko, T.-A.; Ishiyama, T.; Miyaura, N. A Sequence of Palladium-Catalyzed Borylation of Allyl Acetates with Bis(pinacolato)diboron and Intramolecular Allylboration for the Cyclization of Oxo-2Alkenyl Acetates. Chem. Lett. 1997, 811−812. (713) Kabalka, G. W.; Venkataiah, B.; Dong, G. Pd-Catalyzed CrossCoupling of Baylis-Hillman Acetate Adducts with Bis(pinacolato)diboron: An Efficient Route to Functionalized Allyl Borates. J. Org. Chem. 2004, 69, 5807−5809. (714) Ramachandran, P. V.; Pratihar, D.; Biswas, D.; Srivastava, A.; Ram Reddy, M. V. Novel Functionalized Trisubstituted Allylboronates BM


Chemical Reviews

Review

via Hosomi-Miyaura Borylation of Functionalized Allyl Acetates. Org. Lett. 2004, 6, 481−484. (715) Kabalka, G. W.; Venkataiah, B.; Dong, G. Baylis-Hillman Chemistry. A One-Pot Cross-Coupling/Allylboration Reaction. Tetrahedron Lett. 2005, 46, 4209−4211. (716) Ito, H.; Kawakami, C.; Sawamura, M. Copper-Catalyzed γSelective and Stereospecific Substitution Reaction of Allylic Carbonates with Diboron: Efficient Route to Chiral Allylboron Compounds. J. Am. Chem. Soc. 2005, 127, 16034−16035. (717) Ito, H.; Ito, S.; Sasaki, Y.; Matsuura, K.; Sawamura, M. CopperCatalyzed Enantioselective Substitution of Allylic Carbonates with Diboron: An Efficient Route to Optically Active α-Chiral Allylboronates. J. Am. Chem. Soc. 2007, 129, 14856−14857. (718) Guzman-Martinez, A.; Hoveyda, A. H. Enantioselective Synthesis of Allylboronates Bearing a Tertiary or Quaternary BSubstituted Stereogenic Carbon by NHC-Cu-Catalyzed Substitution Reactions. J. Am. Chem. Soc. 2010, 132, 10634−10637. (719) Ito, H.; Miya, T.; Sawamura, M. Practical Procedure for Copper(I)-Catalyzed Allylic Boryl Substitution with Stoichiometric Alkoxide Base. Tetrahedron 2012, 68, 3423−3427. (720) Ito, H.; Okura, T.; Matsuura, K.; Sawamura, M. Desymmetrization of meso-2-Alkene-1,4-diol Derivatives through Copper(I)Catalyzed Asymmetric Boryl Substitution and Stereoselective Allylation of Aldehydes. Angew. Chem., Int. Ed. 2010, 49, 560−563. (721) Yamamoto, E.; Takenouchi, Y.; Ozaki, T.; Miya, T.; Ito, H. Copper(I)-Catalyzed Enantioselective Synthesis of α-Chiral Linear or Carbocyclic (E)-(γ-Alkoxyallyl)boronates. J. Am. Chem. Soc. 2014, 136, 16515−16521. (722) Ito, H.; Kosaka, Y.; Nonoyama, K.; Sasaki, Y.; Sawamura, M. Synthesis of Optically Active Boron-Silicon Bifunctional Cyclopropane Derivatives through Enantioselective Copper(I)-Catalyzed Reaction of Allylic Carbonates with a Diboron Derivative. Angew. Chem., Int. Ed. 2008, 47, 7424−7427. (723) Ito, H.; Toyoda, T.; Sawamura, M. Stereospecific Synthesis of Cyclobutylboronates through Copper(I)-Catalyzed Reaction of Homoallylic Sulfonates and a Diboron Derivative. J. Am. Chem. Soc. 2010, 132, 5990−5992. (724) Ito, H.; Sasaki, Y.; Sawamura, M. Copper(I)-Catalyzed Substitution of Propargylic Carbonates with Diboron: Selective Synthesis of Multisubstituted Allenylboronates. J. Am. Chem. Soc. 2008, 130, 15774−15775. (725) Zhao, T. S. N.; Yang, Y. Z.; Lessing, T.; Szabó, K. J. Borylation of Propargylic Substrates by Bimetallic Catalysis. Synthesis of Allenyl, Propargylic, and Butadienyl Bpin Derivatives. J. Am. Chem. Soc. 2014, 136, 7563−7566. (726) Yang, Y. Z.; Szabó, K. J. Synthesis of Allenes by Catalytic Coupling of Propargyl Carbonates with Aryl Iodides in the Presence of Diboron Species. J. Org. Chem. 2016, 81, 250−255. (727) Ito, H.; Kunii, S.; Sawamura, M. Direct Enantio-Convergent Transformation of Racemic Substrates Without Racemization or Symmetrization. Nat. Chem. 2010, 2, 972−976. (728) Park, J. K.; Lackey, H. H.; Ondrusek, B. A.; McQuade, D. T. Stereoconvergent Synthesis of Chiral Allylboronates from an E/Z Mixture of Allylic Aryl Ethers Using a 6-NHC-Cu(I) Catalyst. J. Am. Chem. Soc. 2011, 133, 2410−2413. (729) Park, J. K.; McQuade, D. T. Chiral 6-NHC Ligand and Copper Complex: Properties, Application, and Mechanism. Synthesis 2012, 44, 1485−1490. (730) Park, J. K.; McQuade, D. T. Iterative Asymmetric Allylic Substitutions: syn- and anti-1,2-Diols through Catalyst Control. Angew. Chem., Int. Ed. 2012, 51, 2717−2721. (731) Olsson, V. J.; Sebelius, S.; Selander, N.; Szabó, K. J. Direct Boronation of Allyl Alcohols with Diboronic Acid Using Palladium Pincer-Complex Catalysis. A Remarkably Facile Allylic Displacement of the Hydroxy Group under Mild Reaction Conditions. J. Am. Chem. Soc. 2006, 128, 4588−4589. (732) Selander, N.; Kipke, A.; Sebelius, S.; Szabó, K. J. Petasis Borono-Mannich Reaction and Allylation of Carbonyl Compounds via Transient Allyl Boronates Generated by Palladium-Catalyzed Sub-

stitution of Allyl Alcohols. An Efficient One-Pot Route to Stereodefined α-Amino Acids and Homoallyl Alcohols. J. Am. Chem. Soc. 2007, 129, 13723−13731. (733) Selander, N.; Paasch, J. R.; Szabó, K. J. Palladium-Catalyzed Allylic C−OH Functionalization for Efficient Synthesis of Functionalized Allylsilanes. J. Am. Chem. Soc. 2011, 133, 409−411. (734) Dutheuil, G.; Selander, N.; Szabó, K. J.; Aggarwal, V. K. Direct Synthesis of Functionalized Allylic Boronic Esters from Allylic Alcohols and Inexpensive Reagents and Catalysts. Synthesis 2008, 2293−2297. (735) Larsson, J. M.; Szabó, K. J. Mechanistic Investigation of the Palladium-Catalyzed Synthesis of Allylic Silanes and Boronates from Allylic Alcohols. J. Am. Chem. Soc. 2013, 135, 443−455. (736) Selander, N.; Szabó, K. J. Performance of SCS Palladium Pincer Complexes in Borylation of Allylic Alcohols. Control of the Regioselectivity in the One-Pot Borylation-Allylation Process. J. Org. Chem. 2009, 74, 5695−5698. (737) Selander, N.; Szabó, K. J. Single-Pot Triple Catalytic Transformations Based on Coupling of In Situ Generated Allyl Boronates with In Situ Hydrolyzed Acetals. Chem. Commun. 2008, 3420−3422. (738) Selander, N.; Szabó, K. J. Synthesis of Stereodefined Substituted Cycloalkenes by a One-Pot Catalytic Boronation− Allylation−Metathesis Sequence. Adv. Synth. Catal. 2008, 350, 2045−2051. (739) Raducan, M.; Alam, R.; Szabó, K. J. Palladium-Catalyzed Synthesis and Isolation of Functionalized Allylboronic Acids: Selective, Direct Allylboration of Ketones. Angew. Chem., Int. Ed. 2012, 51, 13050−13053. (740) Miralles, N.; Alam, R.; Szabó, K. J.; Fernández, E. TransitionMetal-Free Borylation of Allylic and Propargylic Alcohols. Angew. Chem., Int. Ed. 2016, 55, 4303−4307. (741) Ishiyama, T.; Oohashi, Z.; Ahiko, T.-A.; Miyaura, N. Nucleophilic Borylation of Benzyl Halides with Bis(pinacolato)diboron Catalyzed by Palladium(0) Complexes. Chem. Lett. 2002, 780−781. (742) Joshi-Pangu, A.; Ma, X.; Diane, M.; Iqbal, S.; Kribs, R. J.; Huang, R.; Wang, C.-Y.; Biscoe, M. R. Palladium-Catalyzed Borylation of Primary Alkyl Bromides. J. Org. Chem. 2012, 77, 6629−6633. (743) Cao, Z. C.; Luo, F. X.; Shi, W. J.; Shi, Z. J. Direct Borylation of Benzyl Alcohol and Its Analogues in the Absence of Bases. Org. Chem. Front. 2015, 2, 1505−1510. (744) Fleury-Brégeot, N.; Oehlrich, D.; Rombouts, F.; Molander, G. A. Suzuki−Miyaura Cross-Coupling of Potassium Dioxolanylethyltrifluoroborate and Aryl/Heteroaryl Chlorides. Org. Lett. 2013, 15, 1536−1539. (745) Fleury-Brégeot, N.; Presset, M.; Beaumard, F.; Colombel, V.; Oehlrich, D.; Rombouts, F.; Molander, G. A. Suzuki−Miyaura CrossCoupling of Potassium Alkoxyethyltrifluoroborates: Access to Aryl/ Heteroarylethyloxy Motifs. J. Org. Chem. 2012, 77, 10399−10408. (746) Presset, M.; Fleury-Brégeot, N.; Oehlrich, D.; Rombouts, F.; Molander, G. A. Synthesis and Minisci Reactions of Organotrifluoroborato Building Blocks. J. Org. Chem. 2013, 78, 4615−4619. (747) Amani, J.; Molander, G. A. Toward Efficient Nucleophilic Azaborine Building Blocks for the Synthesis of B-N Naphthyl (Hetero)arylmethane lsosteres. Org. Lett. 2015, 17, 3624−3627. (748) Dudnik, A. S.; Fu, G. C. Nickel-Catalyzed Coupling Reactions of Alkyl Electrophiles, including Unactivated Tertiary Halides, to Generate Carbon-Boron Bonds. J. Am. Chem. Soc. 2012, 134, 10693− 10697. (749) Cheung, M. S.; Sheong, F. K.; Marder, T. B.; Lin, Z. Y. Computational Insight into Nickel-Catalyzed Carbon-Carbon versus Carbon-Boron Coupling Reactions of Primary, Secondary, and Tertiary Alkyl Bromides. Chem. - Eur. J. 2015, 21, 7480−7488. (750) Yang, C.-T.; Zhang, Z.-Q.; Tajuddin, H.; Wu, C.-C.; Liang, J.; Liu, J.-H.; Fu, Y.; Czyzewska, M.; Steel, P. G.; Marder, T. B.; Liu, L. Alkylboronic Esters from Copper-Catalyzed Borylation of Primary and Secondary Alkyl Halides and Pseudohalides. Angew. Chem., Int. Ed. 2012, 51, 528−532. BN


Chemical Reviews

Review

(751) Ito, H.; Kubota, K. Copper(I)-Catalyzed Boryl Substitution of Unactivated Alkyl Halides. Org. Lett. 2012, 14, 890−893. (752) Iwamoto, H.; Kubota, K.; Yamamoto, E.; Ito, H. Copper(I)Catalyzed Carbon-Halogen Bond-Selective Boryl Substitution of Alkyl Halides Bearing Terminal Alkene Moieties. Chem. Commun. 2015, 51, 9655−9658. (753) Liu, M. Y.; Hong, S. B.; Zhang, W.; Deng, W. Expedient Copper-Catalyzed Borylation Reactions Using Amino Acids as Ligands. Chin. Chem. Lett. 2015, 26, 373−376. (754) Kim, J. H.; Chung, Y. K. Copper Nanoparticle-Catalyzed Borylation of Alkyl Bromides with an Organodiboron Compound. RSC Adv. 2014, 4, 39755−39758. (755) Zhou, X. F.; Wu, Y. D.; Dai, J. J.; Li, Y. J.; Huang, Y.; Xu, H. J. Borylation of Primary and Secondary Alkyl Bromides Catalyzed by Cu2O Nanoparticles. RSC Adv. 2015, 5, 46672−46676. (756) Gong, T.-J.; Jiang, Y.-Y.; Fu, Y. Rh(I)-Catalyzed Borylation of Primary Alkyl Chlorides. Chin. Chem. Lett. 2014, 25, 397−400. (757) Bose, S. K.; Fucke, K.; Liu, L.; Steel, P. G.; Marder, T. B. ZincCatalyzed Borylation of Primary, Secondary and Tertiary Alkyl Halides with Alkoxy Diboron Reagents at Room Temperature. Angew. Chem., Int. Ed. 2014, 53, 1799−1803. (758) Atack, T. C.; Lecker, R. M.; Cook, S. P. Iron-Catalyzed Borylation of Alkyl Electrophiles. J. Am. Chem. Soc. 2014, 136, 9521− 9523. (759) Bauer, I.; Knolker, H. J. Iron Catalysis in Organic Synthesis. Chem. Rev. 2015, 115, 3170−3387. (760) Ursinyova, N.; Bedford, R. B.; Gallagher, T. Copper-Catalyzed Borylation of Cyclic Sulfamidates: Access to Enantiomerically Pure (βand γ-Aminoalkyl)boronic Esters. Eur. J. Org. Chem. 2016, 2016, 673− 677. (761) Takahashi, K.; Takagi, J.; Ishiyama, T.; Miyaura, N. Synthesis of 1-Alkenylboronic Esters via Palladium-Catalyzed Cross-Coupling Reaction of Bis(pinacolato)diboron with 1-Alkenyl Halides and Triflates. Chem. Lett. 2000, 126−127. (762) Takagi, J.; Takahashi, K.; Ishiyama, T.; Miyaura, N. PalladiumCatalyzed Cross-Coupling Reaction of Bis(pinacolato)diboron with 1Alkenyl Halides or Triflates: Convenient Synthesis of Unsymmetrical 1,3-Dienes via the Borylation-Coupling Sequence. J. Am. Chem. Soc. 2002, 124, 8001−8006. (763) Ishiyama, T.; Takagi, J.; Kamon, A.; Miyaura, N. PalladiumCatalyzed Cross-Coupling Reaction of Bis(pinacolato)diboron with Vinyl Triflates β-Substituted by a Carbonyl Group: Efficient Synthesis of β-Boryl-α,β-Unsaturated Carbonyl Compounds and Their Synthetic Utility. J. Organomet. Chem. 2003, 687, 284−290. (764) Takagi, J.; Kamon, A.; Ishiyama, T.; Miyaura, N. Synthesis of βBoryl-α,β-Unsaturated Carbonyl Compounds via Palladium-Catalyzed Cross-Coupling Reaction of Bis(pinacolato)diboron with Vinyl Triflates. Synlett 2002, 1880−1882. (765) Eastwood, P. R. A Versatile Synthesis of 4-Aryltetrahydropyridines via Palladium Mediated Suzuki Cross-Coupling with Cyclic Vinyl Boronates. Tetrahedron Lett. 2000, 41, 3705−3708. (766) Suero, M. G.; Bayle, E. D.; Collins, B. S. L.; Gaunt, M. J. Copper-Catalyzed Electrophilic Carbofunctionalization of Alkynes to Highly Functionalized Tetrasubstituted Alkenes. J. Am. Chem. Soc. 2013, 135, 5332−5335. (767) Xue, F.; Zhu, Y.; Li, C. G. Development of an Efficient Process for 3,6-Dihydro-2H-Pyran-4-Boronic Acid Pinacol Ester. Heterocycles 2015, 91, 1654−1659. (768) Huang, K.; Yu, D. G.; Zheng, S. F.; Wu, Z. H.; Shi, Z. J. Borylation of Aryl and Alkenyl Carbamates through Ni-Catalyzed C−O Activation. Chem. - Eur. J. 2011, 17, 786−791. (769) Hata, T.; Kitagawa, H.; Masai, H.; Kurahashi, T.; Shimizu, M.; Hiyama, T. Geminal Difunctionalization of Alkenylidene-type Carbenoids by Using Interelement Compounds. Angew. Chem., Int. Ed. 2001, 40, 790−792. (770) Kurahashi, T.; Hata, T.; Masai, H.; Kitagawa, H.; Shimizu, M.; Hiyama, T. Geminal Dimetalation of Alkylidene-Type Carbenoids with Silylboranes and Diborons. Tetrahedron 2002, 58, 6381−6395.

(771) Shimizu, M.; Nakamaki, C.; Shimono, K.; Schelper, M.; Kurahashi, T.; Hiyama, T. Stereoselective Cross-Coupling Reaction of 1,1-Diboryl-1-alkenes with Electrophiles: A Highly Stereocontrolled Approach to 1,1,2-Triaryl-1-alkenes. J. Am. Chem. Soc. 2005, 127, 12506−12507. (772) Shimizu, M.; Kurahashi, T.; Hiyama, T. Novel Synthesis of 2,3Bisboryl-1,3-dienes from 1-Bromo-1-lithioethene and 1,1-Bisborylalkenes. Synlett 2001, 1006−1008. (773) Kabalka, G. W.; Yao, M.-L. Synthesis of 1-Amino-3[(dihydroxyboryl)methyl]cyclobutanecarboxylic Acid as a Potential Therapy Agent. J. Org. Chem. 2004, 69, 8280−8286. (774) Hashim, J.; Glasnov, T. N.; Kremsner, J. M.; Kappe, C. O. Symmetrical Bisquinolones via Metal-Catalyzed Cross-Coupling and Homocoupling Reactions. J. Org. Chem. 2006, 71, 1707−1710. (775) Chen, L.; Mahmoud, S. M.; Yin, X.; Lalancette, R. A.; Pietrangelo, A. Decreasing Aromaticity in π-Conjugated Materials: Efficient Synthesis and Electronic Structure Identification of Cyclopentadiene-Containing Systems. Org. Lett. 2013, 15, 5970−5973. (776) Kabalka, G. W.; Akula, M. R.; Zhang, J. A Facile Synthesis of Radioiodinated (Z)-Vinyl Iodides via Vinylboronates. Nucl. Med. Biol. 2003, 30, 369−372. (777) Ghosh, S.; Kinney, W. A.; Gauthier, D. A.; Lawson, E. C.; Hudlicky, T.; Maryanoff, B. E. Convenient Preparation of ArylSubstituted Nortropanes by Suzuki−Miyaura Methodology. Can. J. Chem. 2006, 84, 555−560. (778) Occhiato, E. G.; Lo Galbo, F.; Guarna, A. Preparation and Suzuki−Miyaura Coupling Reactions of Tetrahydropyridine-2-boronic Acid Pinacol Esters. J. Org. Chem. 2005, 70, 7324−7330. (779) Merino, P.; Tejero, T. Expanding the Limits of Organoboron Chemistry: Synthesis of Functionalized Arylboronates. Angew. Chem., Int. Ed. 2010, 49, 7164−7165. (780) Hall, D. G. Boronic Acids-Preparation, Applications in Organic Synthesis and Medicine; Wiley-VCH: Weinheim, 2005. (781) Chow, W. K.; Yuen, O. Y.; Choy, P. Y.; So, C. M.; Lau, C. P.; Wong, W. T.; Kwong, F. Y. A Decade Advancement of Transition Metal-Catalyzed Borylation of Aryl Halides and Sulfonates. RSC Adv. 2013, 3, 12518−12539. (782) Wang, Y.; Song, J.; Xu, L.; Kan, Y.; Shi, J.; Wang, H. Synthesis and Characterization of Cyclooctatetrathiophenes with Different Connection Sequences. J. Org. Chem. 2014, 79, 2255−2262. (783) Ishiyama, T.; Murata, M.; Miyaura, N. Palladium(0)-Catalyzed Cross-Coupling Reaction of Alkoxydiboron with Haloarenes: A Direct Procedure for Arylboronic Esters. J. Org. Chem. 1995, 60, 7508−7510. (784) Sumimoto, M.; Iwane, N.; Takahama, T.; Sakaki, S. Theoretical Study of Transmetalation Process in Palladium-Catalyzed Borylation of Iodobenzene with Diboron. J. Am. Chem. Soc. 2004, 126, 10457− 10471. (785) Wei, C. S.; Davies, G. H. M.; Soltani, O.; Albrecht, J.; Gao, Q.; Pathirana, C.; Hsiao, Y.; Tummala, S.; Eastgate, M. D. The Impact of Palladium(II) Reduction Pathways on the Structure and Activity of Palladium(0) Catalysts. Angew. Chem., Int. Ed. 2013, 52, 5822−5826. (786) Berg, C.; Braun, T.; Laubenstein, R.; Braun, B. PalladiumMediated Borylation of Pentafluorosulfanyl Functionalized Compounds: the Crucial Role of Metal Fluorido Complexes. Chem. Commun. 2016, 52, 3931−3934. (787) Piettre, S. R.; Baltzer, S. A New Approach to the Solid-Phase Suzuki Coupling Reaction. Tetrahedron Lett. 1997, 38, 1197−1200. (788) Kim, T. H.; Hangauer, D. G. Polymer-Bound Boronate via the Solid Phase Coupling Reaction of Resin-Bound Aryl Triflate with Diboron Pinacol Ester. Bull. Korean Chem. Soc. 2000, 21, 757−758. (789) Lee, Y.; Kelly, M. J. Solid-Phase Synthesis of Phenols and Pyridinones via Arylboronation/Oxidation Protocol Using Aryl Bromides. Tetrahedron Lett. 2006, 47, 4897−4901. (790) Giroux, A.; Han, Y.; Prasit, P. One Pot Biaryl Synthesis via In Situ Boronate Formation. Tetrahedron Lett. 1997, 38, 3841−3844. (791) Izumi, A.; Nomura, R.; Masuda, T. A New Synthetic Method for Poly(arylene)s Using Bis(pinacolato)Diboron as a Condensation Reagent. Chem. Lett. 2000, 29, 728−729. BO


Chemical Reviews

Review

(792) Shultz, D. A.; Lee, H.; Kumar, R. K.; Gwaltney, K. P. CrossConjugated Bis(porphyrin)s: Synthesis, Electrochemical Behavior, Mixed Valency, and Biradical Dication Formation. J. Org. Chem. 1999, 64, 9124−9136. (793) Deng, Y.; Chang, C. K.; Nocera, D. G. Facile Synthesis of βDerivatized Porphyrins - Structural Characterization of a β-β-bisPorphyrin. Angew. Chem., Int. Ed. 2000, 39, 1066−1068. (794) Yu, H.-B.; Hu, Q.-S.; Pu, L. The First Optically Active BINOLBINAP Copolymer Catalyst: Highly Stereoselective Tandem Asymmetric Reactions. J. Am. Chem. Soc. 2000, 122, 6500−6501. (795) Yu, H.-B.; Hu, Q.-S.; Pu, L. Synthesis of a Rigid and Optically Active Poly(BINAP) and Its Application in Asymmetric Catalysis. Tetrahedron Lett. 2000, 41, 1681−1685. (796) Aspley, C. J.; Gareth Williams, J. A. Palladium-Catalysed CrossCoupling Reactions of Ruthenium Bis-terpyridyl Complexes: Strategies for the Incorporation and Exploitation of Boronic Acid Functionality. New J. Chem. 2001, 25, 1136−1147. (797) Goodall, W.; Williams, J. A. G. A New, Highly Fluorescent Terpyridine Which Responds to Zinc Ions with a Large Red-Shift in Emission. Chem. Commun. 2001, 2514−2515. (798) Baranoff, E.; Griffiths, K.; Collin, J.-P.; Sauvage, J.-P.; Ventura, B.; Flamigni, L. A Pseudo-Rotaxane Based on an Iridium(III)Copper(I) Dyad. New J. Chem. 2004, 28, 1091−1095. (799) Arm, K. J.; Williams, J. A. G. Boronic Acid-Substituted Metal Complexes: Versatile Building Blocks for the Synthesis of Multimetallic Assemblies. Chem. Commun. 2005, 230−232. (800) Gaviña, P.; Tatay, S. Synthesis of a Novel Ditopic Ligand Incorporating Directly Bonded 1,10-Phenanthroline and 2,2′:6′,2″Terpyridine Units. Tetrahedron Lett. 2006, 47, 3471−3473. (801) Rochester, D. L.; Develay, S.; Zalis, S.; Williams, J. A. G. Localised to Intraligand Charge-Transfer States in Cyclometalated Platinum Complexes: an Experimental and Theoretical Study into the Influence of Electron-Rich Pendants and Modulation of Excited States by Ion Binding. Dalton Trans. 2009, 1728−1741. (802) Jäger, M.; Kumar, R. J.; Görls, H.; Bergquist, J.; Johansson, O. Facile Synthesis of Bistridentate Ru(II) Complexes Based on 2,6Di(quinolin-8-yl)pyridyl Ligands: Sensitizers with Microsecond 3 MLCT Excited State Lifetimes. Inorg. Chem. 2009, 48, 3228−3238. (803) Collin, J.-P.; Durola, F.; Lux, J.; Sauvage, J.-P. A Rapidly Shuttling Copper-Complexed [2]Rotaxane with Three Different Chelating Groups in Its Axis. Angew. Chem., Int. Ed. 2009, 48, 8532−8535. (804) Durola, F.; Lux, J.; Sauvage, J.-P. A Fast-Moving Copper-Based Molecular Shuttle: Synthesis and Dynamic Properties. Chem. - Eur. J. 2009, 15, 4124−4134. (805) Kelber, J.; Achard, M.-F.; Durola, F.; Bock, H. Distorted Arene Core Allows Room-Temperature Columnar Liquid-Crystal Glass with Minimal Side Chains. Angew. Chem., Int. Ed. 2012, 51, 5200−5203. (806) Fuller, A. A.; Hester, H. R.; Salo, E. V.; Stevens, E. P. In Situ Formation and Reaction of 2-Pyridylboronic Esters. Tetrahedron Lett. 2003, 44, 2935−2938. (807) Martin, T.; Laguerre, C.; Hoarau, C.; Marsais, F. Highly Efficient Borylation Suzuki Coupling Process for 4-Bromo-2ketothiazoles: Straightforward Access to Micrococcinate and Saramycetate Esters. Org. Lett. 2009, 11, 3690−3693. (808) Crestey, F.; Lohou, E.; Stiebing, S.; Collot, V.; Rault, S. Protected Indazole Boronic Acid Pinacolyl Esters: Facile Syntheses and Studies of Reactivities in Suzuki−Miyaura Cross-Coupling and Hydroxydeboronation Reactions. Synlett 2009, 615−619. (809) Hutton, C. A.; Skaff, O. A Convenient Preparation of Dityrosine via Miyaura Borylation-Suzuki Coupling of Iodotyrosine Derivatives. Tetrahedron Lett. 2003, 44, 4895−4898. (810) Skaff, O.; Jolliffe, K. A.; Hutton, C. A. Synthesis of the Side Chain Cross-Linked Tyrosine Oligomers Dityrosine, Trityrosine, and Pulcherosine. J. Org. Chem. 2005, 70, 7353−7363. (811) Xie, D. H.; Li, R.; Zhang, D. Q.; Hu, J. N.; Xiao, D. D.; Li, X. Y.; Xiang, Y. J.; Jin, W. S. Palladium-Catalyzed Borylation of mDibromobenzene Derivative and its Applications in One-Pot Tandem Suzuki−Miyaura Arenes Synthesis. Tetrahedron 2015, 71, 8871−8875.

(812) Brouwer, F.; Alma, J.; Valkenier, H.; Voortman, T. P.; Hillebrand, J.; Chiechi, R. C.; Hummelen, J. C. Using Bis(pinacolato)diboron to Improve the Quality of Regioregular Conjugated CoPolymers. J. Mater. Chem. 2011, 21, 1582−1592. (813) Mentzel, U. V.; Tanner, D.; Tonder, J. E. Comparative Study of the Kumada, Negishi, Stille, and Suzuki−Miyaura Reactions in the Synthesis of the Indole Alkaloids Hippadine and Pratosine. J. Org. Chem. 2006, 71, 5807−5810. (814) Nising, C. F.; Schmid, U. K.; Nieger, M.; Brase, S. A New Protocol for the One-Pot Synthesis of Symmetrical Biaryls. J. Org. Chem. 2004, 69, 6830−6833. (815) Fang, H.; Yan, J.; Wang, B. Biaryl Product Formation from Cross-Coupling in Palladium-Catalyzed Borylation of a Boc Protected Aminobromoquinoline Compound. Molecules 2004, 9, 178−184. (816) Zhang, Y.; Gao, J.; Li, W.; Lee, H.; Lu, B. Z.; Senanayake, C. H. Synthesis of 8-Arylquinolines via One-Pot Pd-Catalyzed Borylation of Quinoline-8-yl Halides and Subsequent Suzuki−Miyaura Coupling. J. Org. Chem. 2011, 76, 6394−6400. (817) Firooznia, F.; Gude, C.; Chan, K.; Marcopulos, N.; Satoh, Y. Enantioselective Synthesis of 4-Substituted Phenylalanines by CrossCoupling Reactions. Tetrahedron Lett. 1999, 40, 213−216. (818) Appukkuttan, P.; Van der Eycken, E.; Dehaen, W. Microwave Enhanced Formation of Electron Rich Arylboronates. Synlett 2003, 1204−1206. (819) Baudoin, O.; Guénard, D.; Guéritte, F. Palladium-Catalyzed Borylation of Ortho-Substituted Phenyl Halides and Application to the One-Pot Synthesis of 2,2′-Disubstituted Biphenyls. J. Org. Chem. 2000, 65, 9268−9271. (820) Diemer, V.; Chaumeil, H.; Defoin, A.; Carre, C. Syntheses of Extreme Sterically Hindered 4-Methoxyboronic Acids. Tetrahedron 2010, 66, 918−929. (821) Tang, W.; Keshipeddy, S.; Zhang, Y.; Wei, X.; Savoie, J.; Patel, N. D.; Yee, N. K.; Senanayake, C. H. Efficient Monophosphorus Ligands for Palladium-Catalyzed Miyaura Borylation. Org. Lett. 2011, 13, 1366−1369. (822) Wang, L.; Cui, X.; Li, J.; Wu, Y.; Zhu, Z.; Wu, Y. Synthesis of Biaryls through a One-Pot Tandem Borylation/Suzuki−Miyaura Cross-Coupling Reaction Catalyzed by a Palladacycle. Eur. J. Org. Chem. 2012, 595−603. (823) Wang, L.; Li, J.; Cui, X.; Wu, Y.; Zhu, Z.; Wu, Y. Cyclopalladated Ferrocenylimine as Efficient Catalyst for the Syntheses of Arylboronate Esters. Adv. Synth. Catal. 2010, 352, 2002−2010. (824) Leng, Y.; Yang, F.; Zhu, W.; Zou, D.; Wu, Y.; Cai, R. Facile Synthesis of Arylboronic Esters by Palladacycle-Catalyzed Bromination of 2-Arylbenzoxazoles and Subsequent Borylation of the Brominated Products. Tetrahedron 2011, 67, 6191−6196. (825) Ma, N.; Zhu, Z.; Wu, Y. Cyclopalladated Ferrocenylimine: a Highly Effective Catalyst for the Borylation/Suzuki Coupling Reaction. Tetrahedron 2007, 63, 4625−4629. (826) Xu, C.; Gong, J.-F.; Song, M.-P.; Wu, Y.-J. Catalysis of the Coupling Reaction of Aryl Chlorides with Bis(pinacolato)diboron by Tricyclohexylphosphine-Cyclopalladated Ferrocenylimine Complexes. Transition Met. Chem. 2009, 34, 175−179. (827) Ishiyama, T.; Ishida, K.; Miyaura, N. Synthesis of Pinacol Arylboronates via Cross-Coupling Reaction of Bis(pinacolato)diboron with Chloroarenes Catalyzed by Palladium(0)-Tricyclohexylphosphine Complexes. Tetrahedron 2001, 57, 9813−9816. (828) Billingsley, K. L.; Barder, T. E.; Buchwald, S. L. PalladiumCatalyzed Borylation of Aryl Chlorides: Scope, Applications, and Computational Studies. Angew. Chem., Int. Ed. 2007, 46, 5359−5363. (829) Chow, W. K.; Yuen, O. Y.; So, C. M.; Wong, W. T.; Kwong, F. Y. Carbon-Boron Bond Cross-Coupling Reaction Catalyzed by -PPh2 Containing Palladium-Indolylphosphine Complexes. J. Org. Chem. 2012, 77, 3543−3548. (830) Chen, Y.; Peng, H.; Pi, Y. X.; Meng, T.; Lian, Z. Y.; Yan, M. Q.; Liu, Y.; Liu, S. H.; Yu, G. A. Efficient Phosphine Ligands for the OnePot Palladium-Catalyzed Borylation/Suzuki−Miyaura Cross-Coupling Reaction. Org. Biomol. Chem. 2015, 13, 3236−3242. BP


Chemical Reviews

Review

(831) Li, P. B.; Fu, C. L.; Ma, S. M. Gorlos-Phos for PalladiumCatalyzed Borylation of Aryl Chlorides. Org. Biomol. Chem. 2014, 12, 3604−3610. (832) Fürstner, A.; Seidel, G. Microwave-Assisted Synthesis of Pinacol Boronates from Aryl Chlorides Catalyzed by a Palladium/ Imidazolium Salt System. Org. Lett. 2002, 4, 541−543. (833) Hooper, A.; Zambon, A.; Springer, C. J. A Novel Protocol for the One-Pot Borylation/Suzuki Reaction Provides Easy Access to Hinge-Binding Groups for Kinase Inhibitors. Org. Biomol. Chem. 2016, 14, 963−969. (834) Zhu, L.; Duquette, J.; Zhang, M. An Improved Preparation of Arylboronates: Application in One-Pot Suzuki Biaryl Synthesis. J. Org. Chem. 2003, 68, 3729−3732. (835) Zaidlewicz, M.; Wolan, A. Syntheses with Organoboranes. XIII. Synthesis of ω-(4-Bromophenyl)alkanoic Acids and their Borylation. J. Organomet. Chem. 2002, 657, 129−135. (836) Lu, J.; Guan, Z.-Z.; Gao, J.-W.; Zhang, Z.-H. An Improved Procedure for the Synthesis of Arylboronates by Palladium-Catalyzed Coupling Reaction of Aryl Halides and Bis(pinacolato)diboron in Polyethylene Glycol. Appl. Organomet. Chem. 2011, 25, 537−541. (837) Lipshutz, B. H.; Moser, R.; Voigtritter, K. R. Miyaura Borylations of Aryl Bromides in Water at Room Temperature. Isr. J. Chem. 2010, 50, 691−695. (838) Klumphu, P.; Lipshutz, B. H. “Nok”: A Phytosterol-Based Amphiphile Enabling Transition-Metal-Catalyzed Couplings in Water at Room Temperature. J. Org. Chem. 2014, 79, 888−900. (839) Miura, M.; Koike, T.; Ishihara, T.; Sakamoto, S.; Okada, M.; Ohta, M.; Tsukamoto, S.-I. One-Pot Preparation of Unsymmetrical Biaryls via Suzuki Cross-Coupling Reaction of Aryl Halide Using Phase-Transfer Catalyst in a Biphasic Solvent System. Synth. Commun. 2007, 37, 667−674. (840) Fujihara, T.; Yoshikawa, T.; Satou, M.; Ohta, H.; Terao, J.; Tsuji, Y. N-Heterocyclic Carbene Ligands Bearing Poly(ethylene glycol) Chains: Effect of the Chain Length on Palladium-Catalyzed Coupling Reactions Employing Aryl Chlorides. Chem. Commun. 2015, 51, 17382−17385. (841) Dzhevakov, P. B.; Topchiy, M. A.; Zharkova, D. A.; Morozov, O. S.; Asachenko, A. F.; Nechaev, M. S. Miyaura Borylation and OnePot Two-Step Homocoupling of Aryl Chlorides and Bromides under Solvent-Free Conditions. Adv. Synth. Catal. 2016, 358, 977−983. (842) Bej, A.; Srimani, D.; Sarkar, A. Palladium Nanoparticle Catalysis: Borylation of Aryl and Benzyl Halides and One-Pot Biaryl Synthesis via Sequential Borylation-Suzuki−Miyaura Coupling. Green Chem. 2012, 14, 661−667. (843) Zhu, Y.; Hosmane, N. S. Nanocatalysis: Recent Advances and Applications in Boron Chemistry. Coord. Chem. Rev. 2015, 293−294, 357−367. (844) Gendrineau, T.; Marre, S.; Vaultier, M.; Pucheault, M.; Aymonier, C. Microfluidic Synthesis of Palladium Nanocrystals Assisted by Supercritical CO2: Tailored Surface Properties for Applications in Boron Chemistry. Angew. Chem., Int. Ed. 2012, 51, 8525−8528. (845) Kawamorita, S.; Ohmiya, H.; Iwai, T.; Sawamura, M. Palladium-Catalyzed Borylation of Sterically Demanding Aryl Halides with a Silica-Supported Compact Phosphane Ligand. Angew. Chem., Int. Ed. 2011, 50, 8363−8366. (846) Iwai, T.; Harada, T.; Tanaka, R.; Sawamura, M. Silicasupported Tripod Triarylphosphines: Application to PalladiumCatalyzed Borylation of Chloroarenes. Chem. Lett. 2014, 43, 584−586. (847) Vogels, C. M.; Westcott, S. A. Sterically Demanding Aryl Chlorides: No Longer a Problem for Borylations. ChemCatChem 2012, 4, 47−49. (848) Pandarus, V.; Gingras, G.; Béland, F.; Ciriminna, R.; Pagliaro, M. Fast and Clean Borylation of Aryl Halides Under Flow Using Sol− Gel Entrapped SiliaCat DPP-Pd. Org. Process Res. Dev. 2014, 18, 1556−1559. (849) Pandarus, V.; Gingras, G.; Béland, F.; Ciriminna, R.; Pagliaro, M. Clean and Fast Cross-Coupling of Aryl Halides in One-Pot. Beilstein J. Org. Chem. 2014, 10, 897−901.

(850) Pandarus, V.; Marion, O.; Gingras, G.; Béland, F.; Ciriminna, R.; Pagliaro, M. SiliaCat Diphenylphosphine Palladium(II) Catalyzed Borylation of Aryl Halides. ChemCatChem 2014, 6, 1340−1348. (851) Molander, G. A.; Trice, S. L. J.; Dreher, S. D. PalladiumCatalyzed, Direct Boronic Acid Synthesis from Aryl Chlorides: A Simplified Route to Diverse Boronate Ester Derivatives. J. Am. Chem. Soc. 2010, 132, 17701−17703. (852) Molander, G. A.; Trice, S. L. J.; Kennedy, S. M.; Dreher, S. D.; Tudge, M. T. Scope of the Palladium-Catalyzed Aryl Borylation Utilizing Bis-Boronic Acid. J. Am. Chem. Soc. 2012, 134, 11667−11673. (853) Williams, M. J.; Chen, Q.; Codan, L.; Dermenjian, R. K.; Dreher, S. D.; Gibson, A. W.; He, X.; Jin, Y.; Keen, S. P.; Lee, A.; Lieberman, D.; Lin, W.; Liu, G.; McLaughlin, M.; Reibarkh, M.; Scott, J. P.; Strickfuss, S.; Tan, L.; Varsolona, R. J.; Wen, F. Process Development of the HCV NS5b-site D Inhibitor MK-8876. Org. Process Res. Dev. 2016, DOI: 10.1021/acs.oprd.5b00405. (854) Molander, G. A.; Trice, S. L. J.; Kennedy, S. M. Scope of the Two-Step, One-Pot Palladium-Catalyzed Borylation/Suzuki CrossCoupling Reaction Utilizing Bis-Boronic Acid. J. Org. Chem. 2012, 77, 8678−8688. (855) Molander, G. A.; Trice, S. L. J.; Tschaen, B. A Modified Procedure for the Palladium Catalyzed Borylation/Suzuki−Miyaura Cross-Coupling of Aryl and Heteroaryl Halides Utilizing Bis-Boronic Acid. Tetrahedron 2015, 71, 5758−5764. (856) Molander, G. A.; Cavalcanti, L. N.; García-García, C. NickelCatalyzed Borylation of Halides and Pseudohalides with Tetrahydroxydiboron [B2(OH)4]. J. Org. Chem. 2013, 78, 6427−6439. (857) Magano, J.; Monfette, S. Development of an Air-Stable, Broadly Applicable Nickel Source for Nickel-Catalyzed CrossCoupling. ACS Catal. 2015, 5, 3120−3123. (858) Molander, G. A.; Trice, S. L. J.; Kennedy, S. M. PalladiumCatalyzed Borylation of Aryl and Heteroaryl Halides Utilizing Tetrakis(dimethylamino)diboron: One Step Greener. Org. Lett. 2012, 14, 4814−4817. (859) Bello, C. S.; Schmidt-Leithoff, J. Borylation of Organo Halides and Triflates Using Tetrakis(dimethylamino)diboron. Tetrahedron Lett. 2012, 53, 6230−6235. (860) Kennedy, J. W. J.; Hall, D. G. Design of Chiral BoronateSubstituted Acrylanilides.: Self-Activation and Boron-Transmitted 1,8Stereoinduction in [4 + 2]Cycloaddition. J. Organomet. Chem. 2003, 680, 263−270. (861) Kabalka, G. W.; Akula, M. R.; Zhang, J. Synthesis of Radioiodinated Aryl Iodides via Boronate Precursors. Nucl. Med. Biol. 2002, 29, 841−843. (862) Xu, L.; Li, P. F. Direct Introduction of a Naphthalene-1,8Diamino Boryl [B(dan)] Group by a Pd-Catalysed Selective Boryl Transfer Reaction. Chem. Commun. 2015, 51, 5656−5659. (863) Ratniyom, J.; Dechnarong, N.; Yotphan, S.; Kiatisevi, S. Convenient Synthesis of Arylboronates through a Synergistic Pd/CuCatalyzed Miyaura Borylation Reaction under Atmospheric Conditions. Eur. J. Org. Chem. 2014, 2014, 1381−1385. (864) Yan, G.; Yang, M. H.; Yu, J. Ligand-Free Copper-Catalyzed Borylation of Aryl and Benzyl Halides with Bis(pinacolato)diboron. Lett. Org. Chem. 2012, 9, 71−75. (865) Ando, S.; Matsunaga, H.; Ishizuka, T. A Bicyclic NHeterocyclic Carbene as a Bulky but Accessible Ligand: Application to the Copper-Catalyzed Borylations of Aryl Halides. J. Org. Chem. 2015, 80, 9671−9681. (866) Yamamoto, T.; Morita, T.; Takagi, J.; Yamakawa, T. NiCl2(PMe3)2-Catalyzed Borylation of Aryl Chlorides. Org. Lett. 2011, 13, 5766−5769. (867) Kumar, A.; Bheeter, L. P.; Gangwar, M. K.; Sortais, J.-B.; Darcel, C.; Ghosh, P. Nickel Complexes of 1,2,4-Triazole Derived Amido-Functionalized N-Heterocyclic Carbene Ligands: Synthesis, Theoretical Studies and Catalytic Application. J. Organomet. Chem. 2015, 786, 63−70. (868) Bheeter, L. P.; Wei, D.; Dorcet, V.; Roisnel, T.; Ghosh, P.; Sortais, J.-B.; Darcel, C. 1,2,4-Triazole-Based N-Heterocyclic Carbene BQ


Chemical Reviews

Review

Nickel Complexes - Synthesis and Catalytic Application. Eur. J. Inorg. Chem. 2015, 5226−5231. (869) Bose, S. K.; Marder, T. B. Efficient Synthesis of Aryl Boronates via Zinc-Catalyzed Cross-Coupling of Alkoxy Diboron Reagents with Aryl Halides at Room Temperature. Org. Lett. 2014, 16, 4562−4565. (870) Bose, S. K.; Deißenberger, A.; Eichhorn, A.; Steel, P. G.; Lin, Z.; Marder, T. B. Zinc-Catalyzed Dual C−X and C−H Borylation of Aryl Halides. Angew. Chem., Int. Ed. 2015, 54, 11843−11847. (871) Bose, S. K.; Marder, T. B. A Leap Ahead for Activating C-H Bonds. Science 2015, 349, 473−474. (872) Zhang, J. M.; Wu, H. H.; Zhang, J. L. Cesium Carbonate Mediated Borylation of Aryl Iodides with Diboron in Methanol. Eur. J. Org. Chem. 2013, 6263−6266. (873) Miralles, N.; Romero, R. M.; Fernández, E.; Muñiz, K. A Mild Carbon-Boron Bond Formation from Diaryliodonium Salts. Chem. Commun. 2015, 51, 14068−14071. (874) Chen, K.; Zhang, S.; He, P.; Li, P. Efficient Metal-Free Photochemical Borylation of Aryl Halides under Batch and Continuous-Flow Conditions. Chem. Sci. 2016, 7, 3676−3680. (875) Mfuh, A. M.; Doyle, J. D.; Chhetri, B.; Arman, H. D.; Larionov, O. V. Scalable, Metal- and Additive-Free, Photoinduced Borylation of Haloarenes and Quaternary Arylammonium Salts. J. Am. Chem. Soc. 2016, 138, 2985−2988. (876) Teltewskoi, M.; Panetier, J. A.; MacGregor, S. A.; Braun, T. A Highly Reactive Rhodium(I)-Boryl Complex as a Useful Tool for C-H Bond Activation and Catalytic C-F Bond Borylation. Angew. Chem., Int. Ed. 2010, 49, 3947−3951. (877) Kallane, S. I.; Teltewskoi, M.; Braun, T.; Braun, B. C-H and CF Bond Activations at a Rhodium(I) Boryl Complex: Reaction Steps for the Catalytic Borylation of Fluorinated Aromatics. Organometallics 2015, 34, 1156−1169. (878) Guo, W. H.; Min, Q. Q.; Gu, J. W.; Zhang, X. G. RhodiumCatalyzed ortho-Selective C-F Bond Borylation of Polyfluoroarenes with Bpin-Bpin. Angew. Chem., Int. Ed. 2015, 54, 9075−9078. (879) Niwa, T.; Ochiai, H.; Watanabe, Y.; Hosoya, T. Ni/CuCatalyzed Defluoroborylation of Fluoroarenes for Diverse C−F Bond Functionalizations. J. Am. Chem. Soc. 2015, 137, 14313−14318. (880) Liu, X. W.; Echavarren, J.; Zarate, C.; Martin, R. Ni-Catalyzed Borylation of Aryl Fluorides via C−F Cleavage. J. Am. Chem. Soc. 2015, 137, 12470−12473. (881) Ilchenko, N. O.; Janson, P. G.; Szabó, K. J. Copper-mediated C−H Trifluoromethylation of Quinones. Chem. Commun. 2013, 49, 6614−6616. (882) Zhang, H.; Song, Y.; Zhao, J.; Zhang, J.; Zhang, Q. Regioselective Radical Aminofluorination of Styrenes. Angew. Chem., Int. Ed. 2014, 53, 11079−11083. (883) Chen, J. P.; Zhao, K. Y.; Ge, B. Y.; Xu, C. Y.; Wang, D. W.; Ding, Y. Q. Iridium-Catalyzed Synthesis of Diaryl Ethers by Means of Chemoselective C−F Bond Activation and the Formation of B−F Bonds. Chem. - Asian J. 2015, 10, 468−473. (884) Ishiyama, T.; Itoh, Y.; Kitano, T.; Miyaura, N. Synthesis of Arylboronates via the Palladium(0)-Catalyzed Cross-Coupling Reaction of Tetra(alkoxo)diborons with Aryl Triflates. Tetrahedron Lett. 1997, 38, 3447−3450. (885) Brimble, M. A.; Duncalf, L. J.; Neville, D. Double Furofuran Annulation to a Bis-naphthoquinone: an Approach to Dimeric Pyranonaphthoquinones. J. Chem. Soc., Perkin Trans. 1 1998, 4165− 4174. (886) Brimble, M. A.; Issa, F. Reaction of Bromonaphthofurans with Bis(pinacolato)diboron. Aust. J. Chem. 1999, 52, 1021−1028. (887) Brimble, M. A.; Lai, M. Y. H. Suzuki−Miyaura Homocoupling of Naphthyl Triflates Using Bis(pinacolato)diboron: Approaches to the Biaryl Skeleton of Crisamicin A. Org. Biomol. Chem. 2003, 1, 2084−2095. (888) Fang, H.; Kaur, G.; Yan, J.; Wang, B. An Efficient Synthesis of Sterically Hindered Arylboronic Acids. Tetrahedron Lett. 2005, 46, 1671−1674.

(889) Araki, H.; Katoh, T.; Inoue, M. Synthesis and Reaction of the First Oxazol-4-ylboronates: Useful Reagents for the Preparation of the Oxazole-Containing Biaryl Compounds. Synlett 2006, 555−558. (890) Thompson, A. L.; Kabalka, G. W.; Akula, M. R.; Huffman, J. W. The Conversion of Phenols to the Corresponding Aryl Halides under Mild Conditions. Synthesis 2005, 547−550. (891) Chow, W.-K.; So, C.-M.; Lau, C.-P.; Kwong, F.-Y. PalladiumCatalyzed Borylation of Aryl Mesylates and Tosylates and Their Applications in One-Pot Sequential Suzuki−Miyaura Biaryl Synthesis. Chem. - Eur. J. 2011, 17, 6913−6917. (892) Kinuta, H.; Tobisu, M.; Chatani, N. Rhodium-Catalyzed Borylation of Aryl 2-Pyridyl Ethers through Cleavage of the CarbonOxygen Bond: Borylative Removal of the Directing Group. J. Am. Chem. Soc. 2015, 137, 1593−1600. (893) Kinuta, H.; Hasegawa, J.; Tobisu, M.; Chatani, N. RhodiumCatalyzed Borylation of Aryl and Alkenyl Pivalates through the Cleavage of Carbon-Oxygen Bonds. Chem. Lett. 2015, 44, 366−368. (894) Zarate, C.; Manzano, R.; Martin, R. Ipso-Borylation of Aryl Ethers via Ni-Catalyzed C−OMe Cleavage. J. Am. Chem. Soc. 2015, 137, 6754−6757. (895) Nakamura, K.; Tobisu, M.; Chatani, N. Nickel-Catalyzed Formal Homocoupling of Methoxyarenes for the Synthesis of Symmetrical Biaryls via C−O Bond Cleavage. Org. Lett. 2015, 17, 6142−6145. (896) Willis, D. M.; Strongin, R. M. Palladium-Catalyzed Borylation of Aryldiazonium Tetrafluoroborate Salts. A New Synthesis of Arylboronic Esters. Tetrahedron Lett. 2000, 41, 8683−8686. (897) Ma, Y.; Song, C.; Jiang, W.; Xue, G.; Cannon, J. F.; Wang, X.; Andrus, M. B. Borylation of Aryldiazonium Ions with N-Heterocyclic Carbene-Palladium Catalysts Formed without Added Base. Org. Lett. 2003, 5, 4635−4638. (898) Zhang, J.; Wang, X.; Yu, H.; Ye, J. Sandmeyer-Type Reaction to Pinacol Arylboronates in Water Phase: a Green Borylation Process. Synlett 2012, 23, 1394−1396. (899) Chen, S. S.; Pan, Z. J.; Wang, Y. PPh3-Mediated Borylation of Arenediazonium Salts with Bis(pinacolato)diborane. Z. Naturforsch., B: J. Chem. Sci. 2014, 69, 982−986. (900) Qiu, D.; Mo, F. Y.; Zheng, Z. T.; Zhang, Y.; Wang, J. B. New Developments in Aromatic Halogenation, Borylation, and Cyanation. Chimia 2011, 65, 909−913. (901) Mo, F.; Jiang, Y.; Qiu, D.; Zhang, Y.; Wang, J. B. Direct Conversion of Arylamines to Pinacol Boronates: A Metal-Free Borylation Process. Angew. Chem., Int. Ed. 2010, 49, 1846−1849. (902) Qiu, D.; Jin, L.; Zheng, Z.; Meng, H.; Mo, F.; Wang, X.; Zhang, Y.; Wang, J. B. Synthesis of Pinacol Arylboronates from Aromatic Amines: A Metal-Free Transformation. J. Org. Chem. 2013, 78, 1923− 1933. (903) Lennox, A. J. J.; Lloyd-Jones, G. C. Selection of Boron Reagents for Suzuki−Miyaura Coupling. Chem. Soc. Rev. 2014, 43, 412−443. (904) Qiu, D.; Wang, S.; Tang, S.; Meng, H.; Jin, L.; Mo, F.; Zhang, Y.; Wang, J. B. Synthesis of Trimethylstannyl Arylboronate Compounds by Sandmeyer-Type Transformations and Their Applications in Chemoselective Cross-Coupling Reactions. J. Org. Chem. 2014, 79, 1979−1988. (905) Qiu, D.; Zhang, Y.; Wang, J. B. Direct Synthesis of Arylboronic Pinacol Esters from Arylamines. Org. Chem. Front. 2014, 1, 422−425. (906) Qiu, D.; Meng, H.; Jin, L.; Tang, S.; Wang, S.; Mo, F.; Zhang, Y.; Wang, J. B. Synthesis of Arylboronic Pinacol Esters from Corresponding Arylamines. Org. Synth. 2014, 91, 106−115. (907) Zhu, C.; Yamane, M. Transition-Metal-Free Borylation of Aryltriazene Mediated by BF3·OEt2. Org. Lett. 2012, 14, 4560−4563. (908) Erb, W.; Albini, M.; Rouden, J.; Blanchet, J. Sequential OnePot Access to Molecular Diversity through Aniline Aqueous Borylation. J. Org. Chem. 2014, 79, 10568−10580. (909) Zhao, C. J.; Xue, D.; Jia, Z. H.; Wang, C.; Xiao, J. L. MethanolPromoted Borylation of Arylamines: A Simple and Green Synthetic Method to Arylboronic Acids and Arylboronates. Synlett 2014, 25, 1577−1584. BR


Chemical Reviews

Review

(910) Nelson, H. M.; Williams, B. D.; Miro, J.; Toste, F. D. Enantioselective 1,1-Arylborylation of Alkenes: Merging Chiral Anion Phase Transfer with Pd Catalysis. J. Am. Chem. Soc. 2015, 137, 3213− 3216. (911) Tobisu, M.; Nakamura, K.; Chatani, N. Nickel-Catalyzed Reductive and Borylative Cleavage of Aromatic Carbon−Nitrogen Bonds in N-Aryl Amides and Carbamates. J. Am. Chem. Soc. 2014, 136, 5587−5590. (912) Zhang, H.; Hagihara, S.; Itami, K. Making Dimethylamino a Transformable Directing Group by Nickel-Catalyzed CN Borylation. Chem. - Eur. J. 2015, 21, 16796−16800. (913) Hu, J. F.; Sun, H. Q.; Cai, W. S.; Pu, X. H.; Zhang, Y. M.; Shi, Z. Z. Nickel-Catalyzed Borylation of Aryl- and Benzyltrimethylammonium Salts via C−N Bond Cleavage. J. Org. Chem. 2016, 81, 14−24. (914) Basch, C. H.; Cobb, K. M.; Watson, M. P. Nickel-Catalyzed Borylation of Benzylic Ammonium Salts: Stereospecific Synthesis of Enantioenriched Benzylic Boronates. Org. Lett. 2016, 18, 136−139. (915) Tobisu, M.; Kinuta, H.; Kita, Y.; Rémond, E.; Chatani, N. Rhodium(I)-Catalyzed Borylation of Nitriles through the Cleavage of Carbon−Cyano Bonds. J. Am. Chem. Soc. 2012, 134, 115−118. (916) Kinuta, H.; Kita, Y.; Rémond, E.; Tobisu, M.; Chatani, N. Novel Synthetic Approach to Arylboronates via Rhodium-Catalyzed Carbon-Cyano Bond Cleavage of Nitriles. Synthesis 2012, 44, 2999− 3002. (917) Yan, J.; Bi, S. W.; Zhang, D. J.; Liu, C. B. Theoretical Description for the Rh(I)-Catalyzed Borylation Mechanism of a Typical Aryl Cyanide. J. Organomet. Chem. 2015, 791, 198−203.

BS


Diboron(4) Compounds: From Structural Curiosity to Synthetic

Recommend Documents