Corey-Bakshi-Shibata reduction mechanism

A series of / -hydroxyamide derivatives of salicylic acid and chiral amino alcohols were synthesized to be used as the most effective catalyst for the enantioselective reduction of a prochiral ketone. Different substituted prochiral ketones are reduced to the corresponding secondary alcohols in yields up to 99% and enantiomeric excess up to 86%. The mechanism for this type of catalyst can be explained by considering the reaction mechanism for the Corey-Bakshi-Shibata catalyst. ... 

The pioneering work from Itsuno group [11-14] on stoichiometric 1,2-aminoalcohol-borane complex-mediated borane reduction of ketones led to the discovery of well-defined oxazaborolidine catalyzed asymmetric reduction by Corey and coworkers [15-18]. Known as Corey-Bakshi-Shibata reaction, or CBS reduction, this reaction has become a standard method for making chiral secondary alcohols for complex molecule synthesis [19]. The generally accepted mechanism of this reaction is shown in Fig. 2. Coordination of the electrophilic reductant BH3 to the nitrogen atom of... 

Corey, E. J. Bakshi, R. K. Shibata, S. Highly Enantioselective Borane Reduction of Ketones Catalyzed by Chiral Oxazaborolidines. Mechanism and Synthetic Implications. J. Am. Chem. Soc. 1987,109,5551-5553. 

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