Iron Catalyzed Hydroboration of Aldehydes and Ketones - The Journal

Oct 30, 2017 - Iron Catalyzed Hydroboration of Aldehydes and Ketones. Sem Raj Tamang and Michael Findlater. Department of Chemistry and Biochemistry, ...
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Iron Catalyzed Hydroboration of Aldehydes and Ketones Sem Raj Tamang and Michael Findlater* Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, United States S Supporting Information *

ABSTRACT: We report an operationally convenient room temperature hydroboration of aldehydes and ketones employing Fe(acac)3 as precatalyst. The hydroboration of aldehydes and ketones proceeded efficiently at room temperature to yield, after work up, 1° and 2° alcohols; chemoselective hydroboration of aldehydes over ketones is attained under these conditions. We propose a σ-bond metathesis mechanism in which an Fe−H intermediate is postulated to be a key reactive species.

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elements (Ca,27 Mg,28 Al,29 Sn,30 Ge,30 P,22b Ga,31 and Ge32), and even lanthanides33 have been developed. Herein, we wish to report the first example of an operationally simple Fecatalyzed hydroboration system capable of converting aldehydes and ketones to boronic esters at room temperature. Initially, we examined the catalytic hydroboration of 4′methylacetophenone (1a) with pinacolborane (HBPin). The reaction of 1a with HBPin in THF employing Fe(acac)3 (3a) for 24 h afforded only 10% of reduced product. However, we were delighted to observe the formation of a highly reactive catalytic species upon addition of NaHBEt3 to 3a; the color of the solution changed from red to dark brown upon salt addition. Thus, stirring 1a and HBPin (1.5 equiv) at room temperature for 10 h, after preactivation of 3a, resulted in 72% yield of the desired alcohol product (2a). After 24 h of stirring, yields of up to 84% of 2a could be obtained. The effectiveness of the catalyst was not affected when the filtrate (after filtration of the activated catalyst) was used; 82% of 2a was afforded after 24 h of stirring. Thus, the presence of a homogeneous catalyst is strongly implied. Moreover, evacuating the volatiles upon activation in vacuo at 45 °C for 1 h prior to catalysis did not affect activity either; 84% of 2a was afforded after 24 h of stirring. When the reaction mixture was heated at 50 °C for 1 h, 100% conversion of 4′-methylacetophenone was observed based on TLC analysis. However, we decided to focus upon the exploration of operationally convenient catalytic conditions and chose to pursue all further reactions at room temperature. The catalytic loading of 3a could be reduced to 1 mol % but resulted in only 59% yield of 2a after 24 h at room temperature. It should be noted that NaHBEt3 has previously been shown to activate inert metal precatalysts to afford systems capable of the hydrosilylation of alkenes34 and carbonyl compounds.35 The influence of electronics on the catalytic system was investigated by testing derivatives of the acetylacetonate (acac) ligand (i.e., substituting the R groups on the ligand with electron donating and electron withdrawing moieties). All activated precatalysts (3b, 3d, and 3e) exhibited similar catalytic efficacy except for

wide variety of transition-metal elements are now employed in catalyzing the transformations of organic substrates.1 Precious metals have come to dominate this field; recently, there has been a surge of interest in catalysts based upon first row metal elements.2 This interest is driven by the demands for efficient, cheap, and atom economic chemical transformations. However, the shift from precious to abundant metal catalysis is still in its infancy; earth abundant transitionmetal-catalyzed transformations are yet to be fully understood from both mechanistic and conceptual perspectives. Nonetheless, reactions that were once typically limited to precious metals (arylation,3 alkylation,4 alkenylation,5 hydrosilylation,6 borylation,7 amination,8 and oxidation9) have now been reported employing earth abundant metal replacements.10,2c Efforts to incorporate earth abundant transition metals in catalytic hydroboration have been driven by the key role organoborates play in organic chemistry as synthetic surrogates. A number of catalytic methods have been employed in the synthesis of alkyl and vinyl boronates.11 Metal catalyzed olefin hydroboration using catecholborane and pinacolborane have been widely reported with precious metal complexes (Rh,11b,12 Ru,13 and Ir12b,h,14). These systems have shown remarkable functional group tolerance, excellent regioselectivity, and enantioselectivity.11b,e,15a,12f,g,15b The importance of organoborates has spurred progress in Fe and Co catalyzed hydroboration of olefins. Chirik et al. reported antiMarkovnikov selective hydroboration of olefins catalyzed by bis(imino)pyridine complexes of Fe16 and Co.17 Huang and coworkers reported Fe18 and Co19 complexes supported by PNN ligands with varying R groups (R = t-Bu, i-Pr) on the periphery of the ligand to be active catalysts for olefin hydroboration. The catalytic hydroboration of olefins with similar Fe or Co pincer-type complexes is now wellexplored.20a,4c,20b−e However, such progress is yet to be fully realized in the closely related field of carbonyl hydroboration. Hydroboration of carbonyl compounds into their respective alcohols (1° and 2°) is also an important transformation in organic chemistry.15a,21 While this reaction has been effectively studied using precious metals,22 complexes containing first row transition metals (Cu,23 Mn,24 Ti,25 and Zn26), main group © 2017 American Chemical Society

Received: September 7, 2017 Published: October 30, 2017 12857

DOI: 10.1021/acs.joc.7b02020 J. Org. Chem. 2017, 82, 12857−12862

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The Journal of Organic Chemistry Scheme 3. Scope of Aldehyde Hydroborationa

Fe(dbm)3 (3c) (Scheme 1); side products from coupling of 1a were observed. Unsurprisingly, when FeCl3 was used as the precatalyst, 2a was obtained in only 10% yield. Scheme 1. Model Hydroboration Catalysis of 1a

The scope of ketone substrates amenable to our hydroboration protocol was explored (Scheme 2). Progress of the Scheme 2. Scope of Ketone Hydroborationa a Yield after column chromatography. bGC−MS shows 100% conversion of starting substrate. cYield after T = 10 h.

a

our optimized reaction conditions; aliquots from the reaction mixture were analyzed using 1H NMR spectroscopy.36 The reaction between 4-fluorobenzaldehyde and 4-fluoroacetophenone showed selectivity for hydroboration of the aldehyde. 1H NMR spectroscopy revealed quantitative consumption of 4fluorobenzaldehyde in the reaction mixture after 1 h (Scheme 4a, Figure S52). Similar chemoselectivity was observed in the reaction between benzaldehyde and acetophenone (Scheme 4b). It also proved possible to delineate the effects of varying substrate electronics employing competition experiments. In the first competition reaction (aldehydes), selectivity for electron-withdrawing substituents was observed, employing 4fluorobenzaldehyde, benzaldehyde, and 4-methoxybenzaldehyde based on 1H NMR spectroscopy (Scheme 4c, Figure S55). After 1 h, addition of a further 1.5 equiv of HBpin to the reaction mixture afforded complete conversion of 4-fluorobenzaldehyde and benzaldehyde to reduced products, whereas unreacted 4-methoxybenzaldehyde could still be observed using 1 H NMR spectroscopy. Similarly, the competition reaction for the ketones showed selectivity for electron-poor substrates; 4fluoroacetophenone was favored over acetophenone and 4′methylacetophenone (Scheme 4d, Figure S54). 1H NMR analysis of the intramolecular hydroboration of 3-acetylbenzaldehyde (6) showed selectivity for the aldehyde over the ketone. A mixture of products was observed: 3-acetylbenzyl alcohol (7a) and 1-(3-(hydroxymethyl)phenyl)ethan-1-ol (7b). The selectivity for the acetyl moiety was not observed as 1H spectra showed no evidence of the aldehydic proton (Figure S56). Baran and coworkers recently exploited Fe(acac)3 in C−C bond forming reactions.37−39 Elegant mechanistic studies have suggested that an Fe(acac)3/PhSiH3 catalyst mixture generates, in situ, an Fe−H in which the silane acts as stoichiometric reductant.39,40 Holland and coworkers isolated Fe−H complexes generated by reacting iron chloride complexes with potassium triethylborohydride.41 Interestingly, upon prolonged reaction time the iron hydride complex reacted with BEt3, byproduct, to give an iron dihydridoborate complex. Moreover,

Yield after column chromatography.

reactions was conveniently monitored using 11B NMR spectroscopy and GC−MS sampling of the reaction mixture. In virtually all cases, hydroboration of ketones followed by hydrolysis of the boronate ester afforded the corresponding alcohol in high yield. Examination of several different ketone substrates demonstrated the generality of the hydroboration protocol as, in all cases, yields of 2° alcohols ranged from good to excellent (Scheme 2). Furthermore, introduction of sterically encumbering groups in the substrate did not inhibit product formation as well (compare 2a and 2c). The hydroboration of aldehydes at room temperature also afforded quantitative yields of reduced boronate ester products. Unsurprisingly, an examination of several different aldehyde substrates demonstrated the generality of the hydroboration protocol, as in most cases, yields of 1° alcohols ranged from good to excellent (Scheme 3). The hydroboration of transcinnamaldehyde afforded two products with α,β-unsaturated 3phenyl-2-propene-1-ol (5d) as the major product and 2phenylethanol as the minor product (5.1:1, Figure S34). Sterically encumbering groups in the substrate were also tolerated. Encouraged by our discovery that hydroboration of both aldehydes and ketones could be effected at room temperature, we chose to examine the potential for chemoselectivity. We submitted reaction mixtures of both aldehydes and ketones to 12858

DOI: 10.1021/acs.joc.7b02020 J. Org. Chem. 2017, 82, 12857−12862

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The Journal of Organic Chemistry Scheme 4. Chemoselective Hydroboration Reactions

Scheme 5. Plausible Mechanism for Hydroboration of Carbonyl Compounds

product and regenerates the Fe−H species, closing the catalytic cycle (Scheme 5). In conclusion, the in situ activation of an iron precatalyst affords an operationally convenient method to catalytically hydroborate aldehydes and ketones. This work represents the first iron-catalyzed hydroboration of aldehydes and ketones. The simplicity of this methodology adds to the recent trend of utilizing earth abundant transition metals for applications that were once limited to precious metals. Most importantly, this work highlights the ability of cheap and readily available iron salts to catalyze hydroboration reactions; typically, such transformations are performed using laboriously prepared homogeneous complexes.

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EXPERIMENTAL SECTION

General Considerations. All reagents were purchased from commercial vendors and used without further purification unless otherwise noted. Fe(hfa)3 was prepared according to the literature.43 All preparations were performed under an atmosphere of dry argon using Schlenk and glovebox techniques unless otherwise noted. Solvents (benzene-d6, toluene-d8) were dried over activated molecular sieves (4 Å) prior to usage; CDCl3 was used without drying. 1H, 13C, and 11B NMR spectra were recorded on a Jeol 400 MHz spectrometer at 300 K unless otherwise noted. 1H NMR spectra were referenced to the solvent residual peak (CDCl3, δ 7.26 ppm), and 13C{1H} NMR spectra were referenced to the solvent residual peak (CDCl3, δ 77.16 ppm). 11B NMR spectra were referenced to BF3□OEt2 (δ 0.00 ppm) as external standard. Data for 1H NMR are recorded as follows: the chemical shifts are reported in (δ, ppm), multiplicity (br = broad, s = singlet, d = doublet, t = triplet, m = multiplet, dq = doublet of quartet), and coupling constants in Hz as absolute values. All IR spectra were obtained using a Nicolet iS 5 FT-IR spectrometer equipped with a specac Di Quest ATR accessory in the glovebox. GC−MS data were acquired using Thermo Scientific ISQ Single Quadrupole system. General Procedure for Hydroboration of Ketones to 2° Alcohols (2a−h). A 10 mL oven-dried scintillation vial containing a stir bar was charged with 10 mol % Fe(acac)3 (35.6 mg, 0.1 mmol) and dissolved in THF (1 mL). Ten mol % NaHBEt3 (100 μL, 0.1 mmol, 1.0 M in THF) was then added, and the reaction mixture was stirred for ∼1 min. Ketone (1.0 mmol) and HBpin (1.5 mmol, 192 mg, 218 μL) were then added, and the reaction mixture was stirred at room temperature in the glovebox for 24 h. The reaction mixture was quenched by addition of diethyl ether (10 mL). Subsequently, 3 M NaOH (1 mL) and 30% H2O2 (1 mL) were added, and the reaction mixture was allowed to stir for 1 h at room temperature. The organic layer was extracted with diethyl ether (30 mL) and concentrated under reduced pressure. (Alternative work up method: stir the reaction mixture at 50 °C for 1 h after addition of 1 M HCl (1 mL) and MeOH (3 mL)). After separation of the ether layer, the aqueous layer was

Ritleng and coworkers isolated and reported the structure of the active Ni−H that was formed after addition of KHBEt3 to their Ni catalyst.35 Our attempts to isolate a putative Fe−H have thus far proven unsuccessful. However, our preliminary mechanistic experiments using FTIR suggests the formation of an Fe−H. The broad νB−H band found in NaHBEt3 (1915 cm−1) disappeared upon addition to Fe(acac)3. Concomitantly, a new peak (1701 cm−1) was observed, which we tentatively assigned as arising from the νFe−H band from the in situ generated Fe−H complex (Figure S57). Furthermore, the intensity of the νFe−H band increased when HBpin was added to the activated catalyst in solution; the νB−H band of HBpin (2580 cm−1) completely disappeared (Figure S58). Typically, terminal νM−H bands have been reported to lie between 1900 ± 300 cm−1.42 In related experiments, the addition of acetophenone to the activated precatalyst did not show obvious shifts in the spectra. However, upon addition of HBpin to the mixture of acetophenone/activated precatalyst, the intensity of the carbonyl band (νC = O) at 1680 cm−1 decreased significantly due to the immediate onset of catalyzed hydroboration (Figure S60). These results, in concert with the work of Baran and others,23 lead us to propose a hydroboration mechanism in which generation of an Fe−H plays a key role (Scheme 5). The addition of NaHBEt3 to Fe(acac)3 results in the direct generation of the active Fe−H species in which the hydride is transferred from NaHBEt3. The insertion of the carbonyl substrate to the Fe−H species forms an iron alkoxide intermediate, which subsequently acts with HBPin via σ-bond metathesis. This leads to the formation of the boronate ester 12859

DOI: 10.1021/acs.joc.7b02020 J. Org. Chem. 2017, 82, 12857−12862

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The Journal of Organic Chemistry extracted with diethyl ether (30 mL). The combined organic phases were concentrated under reduced pressure. The crude product was purified by flash column chromatography using ethyl acetate/hexane (1/5) mixture as eluent to afford the desired product. General Procedure for Hydroboration of Aldehydes to 1° Alcohols (5a−j). A 10 mL oven-dried scintillation vial containing a stir bar was charged with 10 mol % Fe(acac)3 (35.6 mg, 0.1 mmol) and dissolved in THF (1 mL). Ten mol % NaHBEt3 (100 μL, 0.1 mmol, 1.0 M in THF) was then added, and the reaction mixture was stirred for ∼1 min. Aldehyde (1.0 mmol) and HBpin (1.5 mmol, 192 mg, 218 μL) were then added, and the reaction mixture was stirred at room temperature in the glovebox for 24 h. The reaction mixture was quenched by addition of diethyl ether (10 mL). Subsequently, 3 M NaOH (1 mL) and 30% H2O2 (1 mL) was added, and the reaction mixture was allowed to stir for 1 h at room temperature. The organic layer was extracted with diethyl ether (30 mL) and concentrated under reduced pressure. (Alternative work up method: stir the reaction mixture at 50 °C for 1 h after addition of 1 M HCl (1 mL) and MeOH (3 mL)). After separation of the ether layer, the aqueous layer was extracted with diethyl ether (30 mL). The combined organic phases were concentrated under reduced pressure. The crude product was purified by flash column chromatography using ethyl acetate/hexane (1/5) mixture as eluent to afford the desired product. General Procedure for Chemoselective Catalytic Hydroboration. A 5 mL oven-dried scintillation vial containing a stir bar was charged with 10 mol % Fe(acac)3 (3.56 mg, 0.01 mmol) and dissolved in THF (1 mL). Ten mol % NaHBEt3 (10 μL, 0.01 mmol, 1.0 M in THF) was then added, and the reaction mixture was stirred for ∼1 min. A separate 5 mL oven-dried scintillation vial was charged with 0.1 mmol aldehyde, 0.1 mmol ketone, and 0.15 mmol (21.8 μL) HBpin. The activated precatalyst reaction mixture was then added to the vial containing the substrates, and the reaction mixture was stirred at room temperature for 1 h. The reaction mixture was quenched by addition of diethyl ether (10 mL). Subsequently, 3 M NaOH (1 mL) and 30% H2O2 (1 mL) were added, and the reaction mixture was allowed to stir for 1 h at room temperature. The organic layer was extracted with diethyl ether (30 mL) and concentrated under reduced pressure. Mesitylene (4.32 mg, 5 μL) (internal standard) and chloroform-d (0.8 mL) was then added to the reaction mixture. The conversion and yield were determined by 1H NMR. General Procedure for Competitive Chemoselective Catalytic Hydroboration of Aldehydes. A 5 mL oven-dried scintillation vial containing a stir bar was charged with 10 mol % Fe(acac)3 (3.56 mg, 0.01 mmol) and dissolved in THF (1 mL). Ten mol % NaHBEt3 (10 μL, 0.01 mmol, 1.0 M in THF) was then added, and the reaction mixture was stirred for ∼1 min. A separate 5 mL oven-dried scintillation vial was charged with benzaldehyde (0.1 mmol, 10.2 μL), 4-methoxy benzaldehyde (0.1 mmol, 12.2 μL), 4-fluorobenzaldehyde (0.1 mmol, 10.7 μL), and HBpin (0.15 mmol, 21.8 μL). The activated precatalyst reaction mixture was then added to the vial containing the substrates, and the reaction mixture was stirred at room temperature for 1 h. An additional 1.5 equiv of HBpin (21.8 μL) was added after 1 h, and the reaction mixture was stirred for another hour. The reaction mixture was quenched by addition of diethyl ether (10 mL). Subsequently, 3 M NaOH (1 mL) and 30% H2O2 (1 mL) were added, and the reaction mixture was allowed to stir for 1 h at room temperature. The organic layer was extracted with diethyl ether (30 mL) and concentrated under reduced pressure. Mesitylene (4.32 mg, 5 μL) (internal standard) and chloroform-d (0.8 mL) were then added to the reaction mixture. The conversion and yield were determined by 1 H NMR. General Procedure for Competitive Chemoselective Catalytic Hydroboration of Ketones. A 5 mL oven-dried scintillation vial containing a stir bar was charged with 10 mol % Fe(acac)3 (3.56 mg, 0.01 mmol) and dissolved in THF (1 mL). Ten mol % NaHBEt3 (10 μL, 0.01 mmol, 1.0 M in THF) was then added, and the reaction mixture was stirred for ∼1 min. A separate 5 mL oven-dried scintillation vial was charged with acetophenone (0.1 mmol, 10.2 μL), 4′-methyl acetophenone (0.1 mmol, 12.2 μL), 4′-fluoroacetophenone (0.1 mmol, 10.7 μL), and HBpin (0.15 mmol, 21.8 μL). The activated

precatalyst reaction mixture was then added to the vial containing the substrates, and the reaction mixture was stirred at room temperature for 1 h. An additional 1.5 equiv of HBpin (21.8 μL) was added after 1 h, and the reaction mixture was stirred for 2 h. The reaction mixture was quenched by addition of diethyl ether (10 mL). Subsequently, 3 M NaOH (1 mL) and 30% H2O2 (1 mL) were added, and the reaction mixture was allowed to stir for 1 h at room temperature. The organic layer was extracted with diethyl ether (30 mL) and concentrated under reduced pressure. Mesitylene (4.32 mg, 5 μL) (internal standard) and chloroform-d (0.8 mL) were then added to the reaction mixture. The conversion and yield were determined by 1H NMR. General Procedure for Intramolecular Hydroboration. A 5 mL oven-dried scintillation vial containing a stir bar was charged with 10 mol % Fe(acac)3 (3.56 mg, 0.01 mmol) and dissolved in THF (1 mL). Ten mol % NaHBEt3 (10 μL, 0.01 mmol, 1.0 M in THF) was then added, and the reaction mixture was stirred for ∼1 min. A separate 5 mL oven-dried scintillation vial was charged with 4acetylbenzaldehyde (0.1 mmol,14.81 mg) and HBpin (0.15 mmol, 21.8 μL). The activated precatalyst reaction mixture was then added to the vial containing the substrates, and the reaction mixture was stirred at room temperature for 1 h. The reaction mixture was quenched by addition of diethyl ether (10 mL). Subsequently, 3 M NaOH (1 mL) and 30% H2O2 (1 mL) were added, and the reaction mixture was allowed to stir for 1 h at room temperature. The organic layer was extracted with diethyl ether (30 mL) and concentrated under reduced pressure. Mesitylene (4.32 mg, 5 μL) (internal standard) and chloroform-d (0.8 mL) were then added to the reaction mixture. The conversion and yield were determined by 1H NMR. Spectral Data for 2° Alcohols. 1-(p-Tolyl)ethanol (2a).22c Yield: 114 mg (84%); colorless oil. δH (400 MHz; CDCl3): 1.49 (3H, d, J = 4.0 Hz), 1.75 (1H, d, J = 4.0 Hz), 2.35 (3H, S), 4.85−4.90 (1H, dq, J = 3.6 Hz), 7.17 (2H, d, J = 8.0 Hz), 7.27 (2H, d, J = 8.0 Hz). 13C{1H} NMR (101 MHz; CDCl3): 143.0, 137.3, 123.0, 125.5, 70.4, 25.2, 21.2. 11 B NMR (128 MHz; CDCl3): 23.6. GC−MS (m/z): 136.15. 1-Phenylethanol (2b).29b Yield: 76 mg (62%); colorless oil. δH (400 MHz; CDCl3): 1.50 (3H, d, J = 6.4 Hz), 1.80 (1H, Br S), 4.91 (1H, q, J = 6.4 Hz), 7.28−7.31 (1H, m), 7.34−7.39 (4H, m). 13C{1H} NMR (101 MHz; CDCl3): 145.9, 128.6, 127.6, 125.5, 70.6, 25.3. 11B NMR (128 MHz; CDCl3): 22.8. GC−MS (m/z): 122.12. 1-(o-Tolyl)ethanol (2c).44 Yield: 113 mg (83%); colorless oil. δH (400 MHz; CDCl3): 1.47 (3H, d, J = 4.0 Hz), 1.69 (1H, d, J = 4.0 Hz), 2.35 (3H, S), 5.11−5.17 (1H, dq, J = 3.6 Hz), 7.12−7.24 (3H, m), 7.52 (1H, d, J = 8.0 Hz). 13C{1H} NMR (101 MHz; CDCl3): 144.0, 134.4, 130.5, 127.3, 126.5, 124.6, 67.0, 24.1, 19.1. 11B NMR (128 MHz; CDCl3): 22.1. GC−MS (m/z): 136.15. 1-(4-(Trifluoromethyl)phenyl)ethanol (2d).45 Yield: 129 mg (68%); colorless oil. δH (400 MHz; CDCl3): 1.51 (3H, d, J = 8.0 Hz), 1.87 (1H, br S), 4.95−5.00 (1H, dq, J = 3.6 Hz), 7.50 (2H, d, J = 8.0 Hz), 7.61 (wH, d, J = 8.0 Hz). 13C{1H} NMR (101 MHz; CDCl3): 149.8, 129.8 (q, J = 32.42 Hz), 125.8, 125.6 (d, J = 3.84 Hz), 123.0, 70.0, 25.6. 11B NMR (128 MHz; CDCl3): 22.2. GC−MS (m/z): 190.12. 1-(4-Fluorophenyl)ethanol (2e).46 Yield: 88 mg (63%); colorless oil. δH (400 MHz; CDCl3): 1.48 (3H, d, J = 4 Hz), 1.78 (1H, br S), 4.87−4.92 (1H, dq, J = 3.6 Hz), 7.03 (2H, t, J = 8.8 Hz), 7.34 (2H, q, J = 5.6 Hz). 13C{1H} NMR (101 MHz; CDCl3): 162.0 (d, JC−F = 265.5 Hz), 141.6(d, JC−F = 2.89 Hz), 127.2 (d, JC−F = 8.68 Hz), 115.4 (d, JC−F = 21.19 Hz), 69.9, 25.4. 11B NMR (128 MHz; CDCl3): 22.3. GC−MS (m/z): 140.13. Diphenylmethanol (2f).22c Yield: 158 mg (86%); white powder. δH (400 MHz; CDCl3): 2.18 (1H, d, J = 4.0 Hz), 5.85 (1H, d, J = 4.0 Hz), 7.25−7.29 (2H, m), 7.32−7.40 (8H, m). 13C{1H} NMR (101 MHz; CDCl3): 143.9, 128.7, 127.7, 126.7, 76.4. 11B NMR (128 MHz; CDCl3): 22.3. GC−MS (m/z): 184.13. 1,1-Diphenylpropan-2-ol (2g).47 Yield: 136 mg (81%); white powder. δH (400 MHz; CDCl3): 1.20 (3H, d, J = 8.0 Hz), 1.64 (1H, d, J = 4.0 Hz), 3.81 (1H, d, J = 8 Hz), 4.52−4.60 (1H, m), 7.17−7.25 (2H, m), 7.28 (4H, d, J = 4.0 Hz), 7.33 (2H, t, J = 8.0 Hz), 7.39 (2H, d, J = 4.0 Hz). 13C{1H} NMR (101 MHz; CDCl3): 142.6, 141.6, 12860

DOI: 10.1021/acs.joc.7b02020 J. Org. Chem. 2017, 82, 12857−12862

The Journal of Organic Chemistry

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129.0, 128.8, 128.3, 127.1, 126.7, 70.2, 60.8, 21.5. 11B NMR (128 MHz; CDCl3): 21.7. GC−MS (M-CH3CO): 168.13. Dicyclohexylmethanol (2h).45 Yield: 176 mg (91%); white powder. δH (400 MHz; CDCl3): 0.96−1.31 (12H, m), 1.39−1.48 (2H, m), 1.66 (2H, d, J = 5.8 Hz), 1.74−1.84 (6H, m), 3.05 (1H, q, J = 5.8 Hz). 13 C{1H} NMR (101 MHz; CDCl3): 80.6, 40.0, 30.1, 27.46, 26.69, 26.63, 26.31. 11B NMR (128 MHz; CDCl3): 22.0. GC−MS (m/z): 196.18. Spectral Data for 1° Alcohols. Naphthalen-1-ylmethanol (5a).45 Yield: 128 mg (81%); Off white powder. δH (400 MHz; CDCl3): 1.73 (1H, t, J = 5.6 Hz), 5.17 (2H, d, J = 6.4 Hz), 7.44−7.58 (4H, m), 7.83 (1H, d, J = 8.8), 7.89 (1H, d, J = 8.4), 8.14 (1H, d, J = 8.4). 13C{1H} NMR (101 MHz; CDCl3): 136.4, 134.0, 131.4, 128.8, 128.8, 126.5, 126.0, 125.55, 125.52, 123.8, 63.9. 11B NMR (128 MHz; CDCl3): 22.5. GC−MS (m/z): 158.21. Benzyl Alcohol (5b).29b Yield: 86 mg (80%); colorless oil. δH (400 MHz; CDCl3): 1.70 (1H, br S), 4.70 (2H, d, J = 6.0 Hz), 7.28−7.33 (1H, m), 7.37 (4H, d, J = 4.8 Hz). 13C{1H} NMR (101 MHz; CDCl3): 141.0, 128.7, 127.77, 127.11, 65.4. 11B NMR (128 MHz; CDCl3): 22.4. GC−MS (m/z): 108.10. 4-Fluorobenzyl Alcohol (5c).29b Yield: 112 mg (89%); colorless oil. δH (400 MHz; CDCl3): 1.68 (1H, br S), 4.66 (2H, d, J = 3.6 Hz), 7.04 (2H, t, J = 7.4 Hz), 7.33 (2H, t, J = 5.8 Hz). 13C{1H} NMR (101 MHz; CDCl3): 162.4 (d, JC−F = 246.53 Hz), 136.7, 128.9 (d, JC−F = 8.69 Hz), 115.4 (d, JC−F = 21.19 Hz), 64.8. 11B NMR (128 MHz; CDCl3): 22.6.GC−MS (m/z): 126.11. 3-Phenyl-2-propene-1-ol (5d).48 Yield: 105 mg (78%); colorless oil. δH (400 MHz; CDCl3): 1.46 (1H, br S), 4.34 (2H, t, J = 5.2 Hz), 6.34−6.41 (1H, m), 6.63 (1H, d, J = 15.6 Hz), 7.23−7.27 (1H, m), 7.33 (2H, t, J = 7.6 Hz), 7.39 (2H, d, J = 7.6 Hz). 13C{1H} NMR (101 MHz; CDCl3): 136.8, 131.3, 128.7, 128.6, 127.9, 126.6, 63.9. 11B NMR (128 MHz; CDCl3): 22.2. GC−MS (m/z): 134.14. 2-Methyl-pentan-1-ol (5e). Characterized by GC−MS. See Figure S73. Cyclohexylmethanol (5f).48 Yield: 80 mg (70%); colorless oil. δH (400 MHz; CDCl3): 0.88−0.98 (2H, m), 1.10−1.30 (4H, m), 1.43− 1.52 (1H, m), 1.66−1.76 (5H, m), 3.44(2H, S). 13C{1H} NMR (101 MHz; CDCl3): 68.9, 40.6, 29.7, 26.7, 26.0. 11B NMR (128 MHz; CDCl3): 22.1. GC−MS (m/z): 114.21 Mesitylmethanol (5g).22c Yield: 127 mg (84%); white powder. δH (400 MHz; CDCl3): 1.56(1H, br S), 2.27 (3H, S), 2.40 (6H, S), 4.72 (2H, d, J = 4.8 Hz), 6.89 (2H, S). 13C{1H} NMR (101 MHz; CDCl3): 137.9, 137.4, 133.9, 129.3, 59.4, 21.1, 19.5. 11B NMR (128 MHz; CDCl3): 21.3. GC−MS (m/z): 151.16. 2,2-Diphenylethanol (5h).47 Yield: 131 mg (66%); white powder. δH (400 MHz; CDCl3): 1.46 (1H, t, J = 6.0 Hz), 4.16- 4.24 (3H, m), 7.22−7.28 (6H, m), 7.31−7.35 (4H, m), 7.00−7.22 (1H, m). 13C{1H} NMR (101 MHz; CDCl3): 141.4, 128.82, 128.40, 126.9, 66.2, 53.7. 11B NMR (128 MHz; CDCl3): 22.1. GC−MS (m/z): 198.13. 2-Methoxybenzyl Alcohol (5i).49 Yield: 117 mg (85%); colorless oil. δH (400 MHz; CDCl3): 2.30 (1H, br S), 3.87 (3H, S), 4.69 (2H, d, J = 6.4 Hz), 6.89 (1H, d, J = 8.4 Hz), 6.95 (1H, t, J = 7.4 Hz), 7.26− 7.31 (2H, m). 13C{1H} NMR (101 MHz; CDCl3): 157.5, 129.1, 129.1, 128.8, 120.8, 110.3, 62.2, 55.4. 11B NMR (128 MHz; CDCl3): 22.4. GC−MS (m/z): 138.13. 4-Methoxybenzyl Alcohol (5j).29b Yield: 115 mg (83%); colorless oil. δH (400 MHz; CDCl3): 1.58 (1H, br S), 3.81 (3H, S), 4.62 (2H, d, J = 6 Hz), 6.90 (2H, d, J = 8 Hz), 7.30 (2H, d, J = 8 Hz). 13C{1H} NMR (101 MHz; CDCl3): 159.3, 133.2, 128.8, 114.1, 65.2, 55.4. 11B NMR (128 MHz; CDCl3):22.3. GC−MS (m/z): 138.11.

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Note

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] ORCID

Michael Findlater: 0000-0003-3738-4039 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support of the Robert A. Welch Foundation (Grant D1807) and the National Science Foundation (Grant CHE1554906) is gratefully acknowledged.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b02020. NMR spectra and GC−MS data (PDF) 12861

DOI: 10.1021/acs.joc.7b02020 J. Org. Chem. 2017, 82, 12857−12862

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