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Pinacolborane

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The reduction of ketones with pinacolborane is catalyzed by NaOt-Bu at ambient temperature. The reaction is high yielding and general, providing complete conversion of aryl and dialkyl ketones. The active hydride source is the trialkoxyborohydride, which is believed to be present in low concentration under the reaction conditions.
I. P. Query, P. A. Squier, E. M. Larson, N. A. Isley, T. B. Clark, J. Org. Chem., 2011, 76, 6452-6456.


Small amounts of n-BuLi catalyze a highly efficient and selective hydroboration of aldehydes and ketones with HBpin. The reaction proceeds rapidly under mild conditions with exceptional functional group compatibility, ample substrate scope, and high selectivity for aldehydes over ketones.
Z. Zhu, X. Wu, X. Xu, Z. Wu, M. Xue, Y. Yao, Q. Shen, X. Bao, J. Org. Chem., 2018, 83, 10677-10683.


Low loadings of AgSbF6 catalyze the hydroboration of nitriles, alkens, and aldehydes under base- and solvent-free conditions. This atom-economic chemoselective protocol shows excellent functional group tolerance and compatibility with structurally and electronically diverse substrates.
V. K. Pandey, C. S. Tiwari, A. Rit, Org. Lett., 2021, 23, 1681-1686.


A nonanuclear copper(II) complex obtained by a facile one-pot self-assembly catalyzes the hydroboration of ketones and aldehydes with the absence of an activator under mild, solvent-free conditions. The air- and moisture-stable catalyst displays high efficiency and chemoselectivity on aldehydes over ketones and ketones over imines.
H. Zeng, J. Wu, S. Li, C. Hui, A. Ta, S.-Y. Cheng, S. Zheng, G. Zhang, Org. Lett., 2019, 21, 401-406.


A recyclable cobalt(II)-terpyridine coordination polymer (CP) is a highly effective hydroboration precatalyst for reductions of ketones, aldehydes, and imines with pinacolborane (HBpin). A wide range of substrates containing polar C=O or C=N bonds have been hydroborated selectively in excellent yields under ambient conditions.
J. Wu, H. Zeng, J. Cheng, S. Zheng, J. A. Golen, D. R. Manke, G. Zhang, J. Org. Chem., 2018, 83, 9442-9448.


Homoleptic cyclopentadienyl lanthanide complexes are excellent catalysts for the hydroboration of various aldehydes and ketones with pinacolborane. These robust lanthanide catalysts exhibited high reactivity with low catalyst loadings under mild conditions, good functional group tolerability, and unique carbonyl-selectivity.
S. Chen, D. Yan, M. Xue, Y. Hong, Y. Yao, Q. Shen, Org. Lett., 2017, 19, 3382-3385.


Chemoselective Luche-Type Reduction of α,β-Unsaturated Ketones by Magnesium Catalysis
Y. K. Jang, M. Magre, M. Rueping, Org. Lett., 2019, 21, 8349-8352.


An operationally convenient hydroboration of aldehydes and ketones employing Fe(acac)3 as precatalyst proceeded efficiently at room temperature to yield, after work up, 1 and 2 alcohols. A σ-bond metathesis mechanism with an Fe-H intermediate as key reactive species is postulated.
S. R. Tamang, M. Findlater, J. Org. Chem., 2017, 82, 12857-12862.


A chiral imidazole iminopyridine as a ligand enables a highly enantioselective cobalt-catalyzed hydroboration of diaryl ketones with pinacolborane to provide chiral benzhydrols in very good yields and ee. This protocol could be carried out in a gram scale under mild reaction conditions with good functional group tolerance.
W. Liu, J. Guo, S. Xing, Z. Lu, Org. Lett., 2020, 22, 2532-2536.


A manganese-catalyzed chemoselective hydroboration of carboxylic acids to the corresponding alcohols offers a high turnover number and turnover frequency at 25C. This method tolerates electronically and sterically differentiated substrates with high chemoselectivity. Importantly, aliphatic long-chain fatty acids, including biomass-derived compounds, can efficiently be reduced.
M. K. Barman, K. Das, B. Maji, J. Org. Chem., 2019, 84, 1570-1579.


The ruthenium complex [(η6-p-cymene){(IMes)P}RuCl] was used for efficient hydroborations of a wide range of nitriles, carboxylic esters, and carboxamides in neat pinacolborane (HBpin) under comparatively mild reaction conditions (60-80 C, 3-5 mol % catalyst loading).
J. Bhattacharjee, D. Blockfeld, M. Tamm, J. Org. Chem., 2022, 87, 1098-1109.


Organoborane reductants have been rendered catalytic through an isodesmic B-O/B-H transborylation applied in the borane-catalyzed, chemoselective alkene reduction and formal hydrofunctionalization of enones. The reaction proceeds via a 1,4-hydroboration of the enone and B-O/B-H transborylation with HBpin, enabling catalyst turnover.
K. Nicholson, T. Langer, S. P. Thomas, Org. Lett., 2021, 23, 2498-2504.


In an operationally simple protocol, a 8-OIQ cobalt complex catalyzes a chemo- and enantioselective 1,4-hydroboration of enones with HBpin to access a broad range of chiral β,β-disubstituted ketones with very good chemo- and enantioselectivties.
X. Ren, Z. Lu, Org. Lett., 2021, 23, 8370-8374.


A combination of KOH and BEt3 catalyzes a deaminative hydroboration of acyl-iminodibenzyl derivatives, including nonheterocyclic carboxamides, to the corresponding amines. This novel transition-metal-free methodology was also applied to the hydroboration/reduction of aldehydes.
W. Yao, J. Wang, A. Zhong, J. Li, J. Yang, Org. Lett., 2020, 22, 8086-8090.


Y[N(TMS)2]3 is an efficient homogeneous catalyst for the hydroboration of secondary amides and tertiary amides to provide the corresponding amines. The reaction tolerates various functional groups such as cyano, nitro, and vinyl groups.
P. Ye, Y. Shao, X. Ye, F. Zhang, R. Li, J. Sun, B. Xu, J. Chen, Org. Lett., 2020, 22, 1265-1269.


Low loadings of AgSbF6 catalyze the hydroboration of nitriles, alkens, and aldehydes under base- and solvent-free conditions. This atom-economic chemoselective protocol shows excellent functional group tolerance and compatibility with structurally and electronically diverse substrates.
V. K. Pandey, C. S. Tiwari, A. Rit, Org. Lett., 2021, 23, 1681-1686.


The ruthenium complex [(η6-p-cymene){(IMes)P}RuCl] was used for efficient hydroborations of a wide range of nitriles, carboxylic esters, and carboxamides in neat pinacolborane (HBpin) under comparatively mild reaction conditions (60-80 C, 3-5 mol % catalyst loading).
J. Bhattacharjee, D. Blockfeld, M. Tamm, J. Org. Chem., 2022, 87, 1098-1109.


A magnesium-catalyzed reduction of linear and cyclic carbamates, including N-Boc protected amines, provides N-methyl amines and amino alcohols which are of significant interest due to their presence in many biologically active molecules. Furthermore, the reduction can be extended to the formation of N-trideuteromethyl labeled amines.
M. Magre, M. Szewczyk, M. Rueping, Org. Lett., 2020, 22, 3209-3214.


A nickel-catalyzed hydroalkylation of enecarbamates (N-Cbz-protected enamines) with alkyl halides provides a wide range of chiral alkyl amines with high regio- and enantioselectivity. The mild conditions lead to high functional group tolerance, which is demonstrated in late-stage modifications of many natural products and drug molecules.
D. Qian, S. Bera, X. Hu, J. Am. Chem. Soc., 2021, 143, 1959-1967.


A complex of a cyclic (alkyl)(amino)carbene (CAAC) ligand with chromium catalyzes a mild, chemoselective, and efficient deoxygenative hydroboration of nitro compounds to provide a broad range of anilines, as well as heteroaryl and aliphatic amine derivatives. The CAAC ligand plays an important role in promoting polarity reversal of hydride of HBpin and serves as an H-shuttle.
L. Zhao, C. Hu, X. Cong, G. Deng, L. L. Liu, M. Luo, X. Zeng, J. Am. Chem. Soc., 2021, 143, 1618-1629.


A chiral phosphoric acid catalyzes an asymmetric transfer hydrogenation of trans-chalcones in the presence of pinacolborane as hydride source. This methodology provides chiral dihydrochalcone derivatives in high yields and with high enantioselectivities under mild conditions.
F. Na, S. S. Lopez, A. Beauseigneur, L. W. Hernandez, Z. Sun, J. C. Antilla, Org. Lett., 2020, 22, 5953-5957.


A copper-catalyzed enantioselective hydroboration of α,β-unsaturated aldehydes with pinacolborane provides the corresponding γ-pinacolboronate alcohols in good yields and enantioselectivities through consecutive hydroboration of the C=O and C=C bonds. The resulting γ-pinacolboronate alcohols could be utilized in various transformations.
W. J. Jang, S. M. Song, Y. Park, J. Yun, J. Org. Chem., 2019, 84, 4429-4434.


A readily available magnesium catalyst achieves a selective hydroboration of a wide range of epoxides and oxetanes yielding secondary and tertiary alcohols in excellent yields and regioselectivities.
M. Magre, E. Paffenholz, B. Maity, L. Cavallo, M. Rueping, J. Am. Chem. Soc., 2020, 142, 14286-14294.


A conjugated bis-guanidinate (CBG)-supported aluminum dihydride complex catalyzes a chemoselective hydroboration of various nitriles and alkynes. The reaction leaves other reducible groups intact. Moreover, aluminum-catalyzed hydroboration is expanded to more challenging substrates such as alkene, pyridine, imine, carbodiimide, and isocyanides.
N. Sarkar, S. Bera, S. Nembenna, J. Org. Chem., 2020, 85, 4999-5009.


A simple [Ru(p-cymene)Cl2]2 complex is used as a catalyst precursor in a catalyzed hydroboration of nitriles and imines using pinacolborane with unprecedented catalytic efficiency.
A. Kaithal, B. Chatterjee, C. Gunanathan, J. Org. Chem., 2016, 81, 11153-11161.


1,2,4,3-triazaphospholenes halides catalyze the 1,2 hydroboration of imines and α,β unsaturated aldehydes with pinacolborane, including examples that did not undergo hydroboration by previously reported diazaphospholene systems. DFT calculations support a mechanism where a triazaphospholene cation interacts with the substrate.
C.-H. Tien, M. R. Adams, M. J. Ferguson, E. R. Johnson, A. W. H. Speed, Org. Lett., 2017, 19, 5565-5568.


A simple [Ru(p-cymene)Cl2]2 complex is used as a catalyst precursor in a catalyzed hydroboration of nitriles and imines using pinacolborane with unprecedented catalytic efficiency.
A. Kaithal, B. Chatterjee, C. Gunanathan, J. Org. Chem., 2016, 81, 11153-11161.


A transition-metal-free semireduction of 3-substituted primary and secondary propiolamides with pinacolborane and catalytic potassium tert-butoxide provides 3-substituted acrylamide derivatives in very good yield with excellent E selectivity. Mechanistic studies suggest that an activated Lewis acid-base complex transfers a hydride to the α-carbon followed by rapid protonation in a trans fashion.
R. J. Grams, C. J. Garcia, C. Szwetkowski, W. L. Santos, Org. Lett., 2020, 22, 7013-7018.


A reductive three-component coupling of terminal alkynes, aryl halides, and pinacolborane provides benzylic alkyl boronates in good yields via a hydrofunctionalization of both π-bonds of the alkyne promoted by cooperative action of the catalysts. The reaction offers excellent substrate scope and tolerates the presence of esters, nitriles, alkyl halides, epoxides, acetals and alkenes.
M. K. Armstrong, G. Lalic, J. Am. Chem. Soc., 2019, 141, 6173-6179.


Copper-Catalyzed Reductive Ireland-Claisen Rearrangements of Propargylic Acrylates and Allylic Allenoates
S. Guo, K. C. Wong, S. Scheeff, Z. He, W. T. K. Chan, K.-H. Low, P. Chiu, J. Org. Chem., 2022, 87, 429-452.


The use of HBpin as a hydrogen source enables a metal-free environmentally benign, simple, and efficient transfer hydrogenation process of quinoxalines to provide the desired tetrahydroquinoxalines in good yields in the presence of Bu4NBr as a noncorrosive and low-cost catalyst.
Q. Guo, J. Chen, G. Shen, G. Lu, X. Yang, Y. Tang, Y. Zhu, S. Wu, B. Fan, J. Org. Chem., 2022, 87, 540-546.