Pinacolborane
Recent Literature
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 boron-functionalized heptaphosphide Zintl cluster catalyzes a transition
metal-free hydroboration of aldehydes and ketones. Moreover, the greenhouse gas
carbon dioxide was efficiently and selectively reduced to methoxyborane.
B. van IJzendoorn, S. F. Albawardi, I. J. Votorica-Yrezabal, G. F. S.
Whitehead, J. E. McGrady, M. Mehta, J. Am. Chem. Soc.,
2022, 144, 21213-21223.
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 25°C. 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 ruthenium-catalyzed hydroboration of ynones provides vinyl
α-hydroxylboronates under mild conditions. This reaction features high
efficiency, a broad scope, and complete chemo-, regio-, and stereoselectivity,
in spite of many possible competitive pathways.
Q. Feng, S. Li, Z. Li, Q. Yan, X. Lin, L. Song, X. Zhang, Y.-D. Wu, J. Sun, J. Am. Chem. Soc.,
2022, 144, 14846-14855.
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.
The use of 9-BBN dimer as a catalyst and pinacolborane as a turnover reagent
enables an efficient hydroboration of nitriles to provide N,N-diborylamines,
which act as efficient synthons for the synthesis of primary amines and
secondary amides.
S. Pradhan, R. V. Sankar, C. Gunanathan, J. Org. Chem., 2022, 87,
12386-12396.
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.