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Quadruple Borylation of Terminal Alkynes Daiki Yukimori, Yuki Nagashima, Chao Wang, Atsuya Muranaka, and Masanobu Uchiyama J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 04 Jun 2019 Downloaded from http://pubs.acs.org on June 4, 2019

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Journal of the American Chemical Society

Quadruple Borylation of Terminal Alkynes Daiki Yukimori,† Yuki Nagashima,*,† Chao Wang,† Atsuya Muranaka,‡ and Masanobu Uchiyama*,†,‡, § †

Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan ‡

Cluster for Pioneering Research (CPR), Advanced Elements Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan §

Research Initiative for Supra-Materials (RISM), Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan

Supporting Information Placeholder ABSTRACT: We present the first quadruple boryla-

tion reaction of terminal alkynes, affording functionalized 1,1,2,2-tetrakis(boronate) derivatives in a chemo-/regio-selective manner. The methodology is operationally simple and a novel B–B bond activation without the need for a transition-metal catalyst.

We report herein a new type of B–B bond activation of bis(pinacolato)diboron (B2(pin)2, pin = O2C2Me4) by the combination of ate complexation and UV light irradiation, enabling the direct quadruple borylation of terminal acetylenes for the first time (Scheme 1). Because of the versatility of organoboron compounds in organic synthesis1 and materials sciences2, the borylation of C–C multiple bonds by B2(pin)2 or pinacolborane (HBpin) has been extensively studied.3 However, relatively little attention has been paid to multiple borylation, and there are only a limited number of examples, involving the Pt(0)-catalyzed diborylation of 1-borylalkenes4a (Scheme 1A) and the base-mediated triple borylation of terminal alkynes4b to afford 1,1,2tris(boronate)s (Scheme 1B). The introduction of four or more boryl groups simultaneously onto a triple bond has not been reported.4c In the course of our work to develop new methodologies for Het–Het bond (Het = B, Si, or Sn) activation and addition to C–C multiple bonds,5 we previously reported an efficient trans-selective diborylation based on pseudo-intramolecular reaction of B2(pin)2, propargyl alcohol, and base. It was anticipated that the initial ate complexation of B2(pin)2 with propargyl alkoxide would lead to enthalpic activation of B–B bond cleavage and entropic stabiliza-

tion of the transition state of C–B bond formation.5b However, simple application of this protocol to terminal alkynes proved unsuccessful due to insufficient activation of the B–B bond by a stable acetylide anion. To overcome this, we envisioned a “photoboost activation strategy” to lower the barrier to B–B bond cleavage. While a number of photo-induced borylation reactions have been developed by utilizing a photo-excited catalyst or photo-generated radical species6, only very limited success has been reported in direct activation of B–B bonds by light irradiation.7 This is because the B–B bond has no absorption in the region beyond 200 nm. Thus, we hypothesized that the introduction of a UV lightabsorbing moiety (such as an aryl acetylene unit) at the diboron center would facilitate cleavage of the B– B bond under UV irradiation. Scheme 1. Multiple Borylation Reactions

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This Work nBuLi

Ar

B2(pin)2

H

Ar

Li

hv

(pin)B Ar

B(pin) B(pin) B(pin) Li

1,1,2,2-tetrakis(boronate) No synthetic method from C–C multiple bond

“Photo-boost Activation”

ΔG

Ar

Ar

Li

Li

B B

B

B B

B–B bond activation

B

Triple Borylation (Previous Work) A) Stepwise borylation Hydroboration R

H

R

B(pin)

B2(cat)2 Pt(dba)3/L

H R

B(pin) B(pin) B(pin) H

1,1,2-tris(boronate)

H R

B(pin) B(pin) B(pin) H

1,1,2-tris(boronate)

then pinacol

B) Direct borylation B2(pin)2, K2CO3 R

H MeOH, Et2O, △

To examine the feasibility of this approach, we focused on the borylation reaction of 4methoxyethynylbenzene (1a) with B2(pin)2. In the absence of light irradiation, 1a was recovered intact under various conditions (Table 1, entry 1). On the other hand, under UV irradiation (λ = 254 nm) at room temperature, the acetylide generated from 1a with a stoichiometric amount of nBuLi in THF formed the ate complex smoothly with 1.5 eq. of B2(pin)2, affording multiply borylated products, such as 1,1,2,2-tetrakis(boronate) (3a) and 1,1,2tris(boronate) (4a) without the need for any catalyst, albeit with low isolated yields (3% and 27%, respectively, Table 1, entry 2).8 The yield of 3a was drastically improved by using a slight excess of B2(pin)2 (2.5–3 eq.) at low concentrations of the reactants in dioxane (entries 3–10). Deprotonation of 1a was mandatory (entry 11), indicating that the initial ate complexation of 1a and B2(pin)2, that is, the introduction of a lightabsorbing moiety at the diboron center, is crucial for the B–B bond activation. The use of MeMgBr gave 3a in comparable yield to that obtained with nBuLi (entry 10 vs 12), whereas NaH gave only a small amount of 3a (entry 13). NaOtBu or nBu3P did not promote this borylation, presumably due to low basicity (entries 14 and 15). Blue LED (λ = 435 nm) irradiation shut down the reaction (entry 16). Finally, the set of conditions shown in entry 10 was found to be optimal. Notably, aliphatic alkynes such as 1-octyne shut down the reaction (entry 17), and this strongly supports the idea that photoactivation of the aryl acetylene moiety initiates B–B bond cleavage and successive C–B bond formation.

B2(pin)2 = bis(pinacolate)diboron. CPME = cyclopentylmethylether. NMR yield determined by 1H NMR analysis (isolated yield in parentheses). a 1-Octyne was used instead of 1a as a starting material.

Table 2. Quadruple Borylation of Terminal Alkynes

Table 1. Optimization of Reaction Conditions


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Journal of the American Chemical Society B2(hexy)=bis(hexyleneglycolato)diboron. Isolated yield (NMR yield in parentheses). a Reaction for 48 h. b Reaction at 100°C for 48 h without UV light irradiation.

With the optimal conditions in hand, we next investigated the scope of the present quadruple borylation reaction (Table 2). A range of terminal aryl alkynes and their analogues could be employed: 1) electron-donating substituents (H, OMe, amino, alkyl and silyl groups) at the para-position of the aryl ring were efficiently converted to the corresponding 1,1,2,2-tetrakis(boronate)s 3a–3h in high yields without formation of undesired side-products, 2) the substituent position (ortho, meta, para, or di-meta) of the methoxy group on the aromatic ring had no effect on the reaction (3a, 3c, 3d, and 3h), 3) electron-withdrawing substituents, such as chloro, phenyl, alkynyl groups, were compatible with the present borylation reaction, affording the desired product in good to excellent yields (3i–3l), 4) the terminal triple bond specificity of this borylation is high, because initial ate complexation is crucial; an internal triple bond was untouched in the case of diyne 1l, affording product 3l chemo-/regio-selectively, and 5) other types of aromatics, including naphthyl and phenanthryl, were applicable (3m and 3n). The use of bis(hexyleneglycolato)diboron was not deleterious to the reaction, and the corresponding 1,1,2,2tetrakis(boronate)s 3p were obtained. On the other hand, 4-bromoethylnylbenzene 1o did not undergo the present borylation, but afforded debrominated by-products, probably because the aromatic C–Br bond is easily decomposed under UV irradiation. As for non-aromatic terminal alkynes, we found that higher reaction temperature (100°C) enabled quadruple borylation to proceed, and primary (1q–1s) and secondary aliphatic substituents (1t) afforded the desired products (3q–3t) in good yields. However, the high temperature was not effective for aryl alkynes, such as 1a, in which afforded complex mixtures. Scheme 2. Effect of In Situ Electrophilic Trapping

Isolated yield. (NMR yield in parentheses)

Scheme 3. Proposed Mechanism and Model Calculation at the UB3LYP/6-31+G*Level (ΔG in kcal/mol) A) Model Calculation of 1st Diborylation λabs < 200 nm O O B B O O

λabs = 276 nm O B O –13.7

B O

Li RT

O B O Li B O O

+26.2 Li

O

O B –34.4

TS1

IM1

B

No Barrier

O B O

B–B bond cleavage & C–B bond formation

B O O

* Li

IM1-S1

B

O

O Li

IM2

Excitation (S0 → S1)

HOMO of IM1

B

O

IM3-S1

B) Proposed Mechanism for Quadruple Borylation Ar

RO B OR B RO

Li OR

1st diborylation

B(OR)2

Li

B(OR)2

Ar B2(OR)2

Ar (RO)2B (RO)2B

E B(OR)2 B(OR)2 IV

E = Li or B(OR)2

B(OR)2

RO B B B(OR)2 RO RO OR

Li

III

II

I

2nd diborylation

Ar

D2O

Ar (RO)2B (RO)2B

D B(OR)2 B(OR)2 3

The present quadruple borylation of 1a under UV irradiation, followed by quenching with D2O, MeOTf, and nBuBr, gave the corresponding deuterated and alkylated products 3aa, 3ab, and 3bc, respectively, in satisfactory yields (Scheme 2). In the thermal borylation by using 1u, an intramolecular cyclization reaction of the quadruple borylated intermediate (2u) with chloro group also proceeded to provide the 1,1,2,2-tetrakis(boronate)cyclopentane (3u). These not only provide experimental evidence that 1lithium 1,1,2,2-tetrakis(boronate) 2 or the corresponding 1-borate equivalent is formed as an intermediate, but also make available a basic architecture to construct variously functionalized 1,1,2,2tetrakis(boronate)s. In order to gain detailed insight into the molecular mechanism of the present reaction, we then performed a model calculation using phenyl acetylide and bis(ethyleneglycolato)diboron (Scheme 3A).



They smoothly form an ate complex (IM1) with a large energy gain (13.7 kcal mol-1). In the ground state, from IM1, the boron vacant orbital approaches the C–C triple bond leading to B–B bond cleavage with an activation energy of 26.2 kcal mol-1. This energy loss is a result of the cleavage of the stable B–B bond. TD-DFT calculation revealed that bis(ethyleneglycolato)diboron has no absorption bands in the region beyond 200 nm, whereas its ate complex (IM1) shows an absorption band corresponding to the S0→S1 transition at 276 nm. Then, we performed geometry optimization of IM1 in the S1 state, revealing smooth B–B bond cleavage without an energy barrier to form IM3-S1. Indeed, participation of the B–B  orbital with the -conjugation of phenyl actetylene in the frontier MOs may also contribute to the photo-induced rapid B–B cleavage (Scheme 3A). Thus, a plausible mechanism for the photoinduced quadruple borylation of terminal aryl acetylenes would be as illustrated in Scheme 3B. As is indicated by the above model calculation (Scheme 3A), IM3-S1 is an intermediary formed by the first photoinduced B–B activation. The vinyl anion intermediate, IM3-S1 is immediately trapped by excess B2(pin)2 to give another borate intermediate III, which undergoes the second B–B activation to afford 1,1,2,2tetrakis(boronate) IV. DFT calculation revealed that the second B–B activation proceeds smoothly with an activation energy of 21.5 kcal mol-1 and a large energy gain (31.7 kcal mol-1) even in the ground state (see Supporting Information). This calculation supports the experimental finding that no intermediate, such as the bis(boronate) derivatives, was detected in the present borylation reaction. Scheme 4. Transformations of the 1,1,2,2Tetrakis(boronate) (3a)

tris(boronate) derivatives, which are versatile platforms for further chemical elaboration (Scheme 4).3,4 1,1,2,2-Tetrakis(boronate) 3a, synthesized from 1a, was treated with 2.5 eq. of NaOtBu in room temperature and then reacted with various electrophiles to give the corresponding tris(boronate)s (4a and 4aa– 4ac) regioselectively in good yields. Since carboanions at the benzyl position are more stable than the terminal alkyl anions, this deboronation proceeds regioselectively at the benzyl position. In summary, we have developed an unprecedented quadruple borylation reaction of terminal alkynes via a novel activation of the stable B–B bond. Two sets of conditions (photo-induced and thermal) were identified for aryl and alkyl alkynes, respectively. This methodology opens up a new access to synthetically challenging 1,1,2,2-tetrakis(boronate)s with high functional group compatibility. We believe that the present protocols might also offer a new approach for the activation of other inert bonds and various Het– Het (Het = B, Si, Sn, etc.) bonds. Efforts to expand the reaction scope and to investigate the physicochemical properties of 1,1,2,2-tetrakis(boronate)s with the help of theoretical and spectroscopic studies are in progress. ASSOCIATED CONTENT The Supporting Information is available free of charge on the ACS Publications website. http://pubs.acs.org. Experimental procedures, analytical data, and computational details (PDF)

AUTHOR INFORMATION Corresponding Author

* [email protected] * [email protected] ORCID

Yuki Nagashima: 0000-0001-8470-5638 Chao Wang: 0000-0002-9165-7758 Atsuya Muranaka: 0000-0002-3246-6003 Masanobu Uchiyama: 0000-0001-6385-5944

ACKNOWLEDGMENT

Isolated yield (NMR yield in parentheses) Conditions: a) H2O (excess), rt; b) D2O (excess), rt; c) allyl bromide (2 eq), rt; d) MeI (2 eq), rt

Finally, we examined whether the functionalized 1,1,2,2-tetrakis(boronate)s could be transformed into

This work was supported by the Sasakawa Scientific Research Grant from The Japan Science Society (No.2019-3002) (to Y. N.), JSPS Grant-in-Aid for Scientific Research on Innovative Areas (No. 17H05430), JSPS KAKENHI (S) (No. 17H06173) (to M.U.). This work was also supported by Nagase Science and Technology Foundation and The Sumitomo Foundation (to M.U.). A generous allotment of computational resources (Projects G18008) from HOKUSAI GreatWave (RIKEN) is gratefully acknowledged.


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REFERENCES (1) (a) Miyaura, N.; Suzuki, A. Palladium-Catalyzed CrossCoupling Reactions of Organoboron Compounds. Chem. Rev. 1995, 95, 2457. (b) Suzuki, A. Cross-Coupling Reactions of Organoboranes: an Easy Way to Construct C–C Bonds (Nobel Lecture). Angew. Chem., Int. Ed. 2011, 50, 6722. (c) Ramachandran, P. V.; Brown, H. C. Recent Advances in Borane Chemistry. ACS Symposium Series 783 Organoboranes for Syntheses; American Chemical Society: Washington DC, 2001. (2) (a) Entwistle, C. D.; Marder, T. B. Boron Chemistry Lights the Way: Optical Properties of Molecular and Polymeric Systems. Angew. Chem., Int. Ed. 2002, 41, 2927. (b) Entwistle, C. D.; Marder, T. B. Applications of Three-Coordinate Organoboron Compounds and Polymers in Optoelectronics. Chem. Mater. 2004, 16, 4574. (c) Zhao, C.-H.; Wakamiya, A.; Inukai, Y.; Yamaguchi, S. Highly Emissive Organic Solids Containing 2,5-Diboryl1,4-phenylene Unit. J. Am. Chem. Soc. 2006, 128, 15934. (d) Baker, S. J.; Ding, C. Z.; Akama, T.; Zhang, Y.-K.; Hernandez, V.; Xia, Y. Therapeutic Potential of Boron-Containing Compounds. Future Med. Chem. 2009, 1, 1275. (e) Smoum, R.; Rubinstein, A.; Dembitsky, V. M.; Srebnik, M. Boron Containing Compounds as Protease Inhibitors. Chem. Rev. 2012, 112, 4156. (f) Diaz, D. B.; Yudin, A. K. The Versatility of Boron in Biological Target Engagement. Nat. Chem. 2017, 9, 731. (3) For reviews on borylations of C–C multiple bond, see: (a) Cuenca, A. B.; Shishido, R., Ito, H.; Fernández, E. TransitionMetal-Free B–B and B–Interelement Reactions with Organic Molecules Chem. Soc. Rev. 2017, 46, 415. (b) Beletskaya, I.; Moberg, C. Element–Element Additions to Unsaturated Carbon– Carbon Bonds Catalyzed by Transition Metal Complexes. Chem. Rev. 2006, 106, 2320. (c) Ansell, M. B.; Navarro, O.; Spencer, J. Transition Metal Catalyzed Element–Element’ Additions to Alkynes. Coord. Chem. Rev. 2017, 336, 54. For recent reviews and examples on the synthesis and reactivities of diborylalkanes, see: (d) Nallagonda, R.; Padala, K.; Masarwa, A. gem-Diborylalkanes: Recent Advances in their Preparation, Transformation and Application. Org. Biomol. Chem. 2018, 16, 1050. (e) Miralles, N.; Maza, R. J.; Fernández, E. Synthesis and Reactivity of 1,1Diborylalkanes towards C–C Bond Formation and Related Mechanisms. Adv. Synth. Catal. 2018, 360, 1306. (f) Yamazaki, A.; Nagao, K.; Iwai, T.; Ohmiya, H.; Sawamura, M. PhosphineCatalyzed anti-Carboboration of Alkynoates with 9-BBN-Based 1,1-Diborylalkanes: Synthesis and Use of Multisubstituted γBorylallylboranes. Angew. Chem., Int. Ed. 2018, 57, 3196. (4) For the synthesis of 1,1,2-tris(boronate)s, see: (a) 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. (b) Gao, G.; Yan, J.; Yang, K.; Chen, F.; Song, Q. Base-Controlled Highly Selective Synthesis of Alkyl 1,2-Bis(boronates) or 1,1,2Tris(boronates) from Terminal Alkynes. Green Chem. 2017, 19, 3997. For the synthesis of 1,1,2,2-tetrakis(boronate)s, see: (c) Zhang, Z.-Q.; Fu, Y.; Xiao, B. Tetraborate Ethanes Compound and Preparation Method Thereof. Patent CN2017/106518899(A). (5) (a) 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.

(b) Nagashima, Y.; Hirano, K.; Takita, R.; Uchiyama, M. transDiborylation of Alkynes: Pseudo-Intramolecular Strategy Utilizing Propargylic Alcohol Unit. J. Am. Chem. Soc. 2014, 136, 8532. (c) Harada, K.; Nogami, M.; Hirano, K.; Kurauchi, D.; Kato, H.; Miyamoto, K.; Saito, T.; Uchiyama, M. Allylic Borylation of Tertiary Allylic Alcohols: A Divergent and Straightforward Access to Allylic Boronates. Org. Chem. Front. 2016, 3, 565. (d) Nagashima, Y.; Yukimori, D.; Wang, C.; Uchiyama, M. In Situ Generation of Silylzinc by Si–B Bond Activation Enabling Silylzincation and Silaboration of Terminal Alkynes. Angew. Chem., Int. Ed. 2018, 57, 8053. (e) Kojima, K.; Nagashima, Y.; Wang, C.; Uchiyama, M. In Situ Generation of Silyl Anion Species with Si–B Bond Activation Allowing Concerted Nucleophilic Aromatic Substitution of Fluoroarenes. ChemPlusChem 2019, 84, 277. (6) For a review, see: (a) Yan, G.; Huang, D. Wu, X. Recent Advances in C–B Bond Formation through a Free Radical Pathway. Adv. Synth. Catal. 2018, 360, 1040. For recent photo-induced borylation reactions without photoredox catalysts, see: (b) 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. (c) Mfuh, A. M.; Nguyen, V. T.; Chhetri, B.; Burch, J. E.; Doyle, J. D.; Nesterov, V. N.; Arman, H. D.; Larionov, O. V. Additive- and Metal-Free, Predictably 1,2- and 1,3Regioselective, Photoinduced Dual C–H/C–X Borylation of Haloarenes. J. Am. Chem. Soc. 2016, 138, 8408. (d) 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. (e) Candish, L.; Teders, M.; Glorius, F. Transition-Metal-Free, Visible-Light-Enabled DecarboxylativeBorylation of Aryl N-Hydroxyphthalimide Esters. J. Am. Chem. Soc. 2017, 139, 7440. (f) Cheng, Y.; Mück-Lichtenfeld, C.; Studer, A. Metal-Free Radical Borylation of Alkyl and Aryl Iodides. Angew. Chem., Int. Ed. 2018, 57, 16832. (g) Cheng, Y.; Mück-Lichtenfeld, C.; Studer, A. Transition Metal-Free 1,2Carboboration of Unactivated Alkenes. J. Am. Chem. Soc. 2018, 140, 6221. (7) Aggarwal and co-workers reported a novel photo-induced B–B bond activation via complex formation between Nhydroxyphthalimide or N-alkylpyridinium and diboron to achieve decarboxylative or deaminative borylation of alkyl amines, see: (a) Fawcett, A.; Pradeilles, J.; Wang, Y.; Mutsuga, T.; Myers, E. L.; Aggarwal, V. K. Photoinduced Decarboxylative Borylation of Carboxylic Acids. Science, 2017, 357, 283. (b) Wu, J.; He, L.; Noble, A.; Aggarwal, V. K. Photoinduced Deaminative Borylation of Alkylamines. J. Am. Chem. Soc. 2018, 140, 10700. Ogawa and co-workers reported a novel photo-induced B–B bond activation enabling organosulfide- or phosphine-catalyzed diborylation of terminal alkynes, see: (c) Yoshimura, A.; Takamachi, Y.; Han, L.-B.; Ogawa, A. Organosulfide-Catalyzed Diboration of Terminal Alkynes under Light. Chem. Eur. J. 2015, 21, 13930. (d) Yoshimura, A.; Takamachi, Y.; Mihara, K.; Saeki, T.; Kawaguchi, S.; Han, L.-B.; Nomoto, A.; Ogawa, A. Photoinduced Metal-Free Diboration of Alkynes in the Presence of Organophosphine Catalysts. Tetrahedron, 2016, 72, 7832. (8) The structures of 3a and 4a were determined by X-ray structural analysis. Structural data can be retrieved from CSD (CCDC 1912516 and 1912517).




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Quadruple Borylation of Terminal Alkynes | Journal of the American

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