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Asymmetric Reduction of Ketones Under Mild Conditions Using NaBH 4 and TarB‐NO 2 : An Efficient and Unusual Chiral Acyloxyborohydride Reducing System
Author(s) -
Cordes David B.,
Nguyen Thao M.,
Kwong Tracey J.,
Suri Jeff T.,
Luibrand Richard T.,
Singaram Bakthan
Publication year - 2005
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200500397
Subject(s) - chemistry , reagent , bifunctional , tartaric acid , enantiomer , reducing agent , lewis acids and bases , combinatorial chemistry , organic chemistry , ketone , enantioselective synthesis , catalysis , citric acid
High enantioselectivities are obtained for the reduction of a series of ketones using the inexpensive and mild reducing agent NaBH 4 with TarB‐NO 2 ( 1 ). This easily prepared tartaric acid‐based reagent combines a Lewis acid with carboxylic acids in a single bifunctional reagent. When combined with NaBH 4 , the resulting chiral acyloxyborohydride mediates the reduction of aromatic ketones to provide the product alcohols in enantiomeric excesses of 93–98 %. Several aliphatic ketones were also reduced with moderate to excellent enantioselectivity. A unique mechanism is provided with supporting calculations for the proposed active species and transition state. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)