Stereoselectivity Corey-Bakshi-Shibata reduction

The use of boranes has attracted considerably more interest over the last several decades and particularly the use of chiral oxazaborolidine catalysts in combination with borane as a stoichiometric reducing agent (the well-known Corey-Bakshi-Shibata (CBS) reduction) (564, 565) represents one of the most important and versatile methods for the stereoselective reduction of prochiral ketones. It is not intended to give a detailed overview of the successful applications of this versatile methodology for complex (natural product) synthesis, as this would be far beyond the scope of this volume. Instead two examples are chosen below to highlight the potential of this method, especially when used for highly selective late-stage modifications (566,567). 

Enantioselective Ketone Reduction. After the pioneering work of Itsuno et al., Corey s group isolated the 1,3,2-oxazaborolidine derived from chiral a,a-diphenyl-2-pyrrolidinemethanol (2) and applied it (and also other related B-alkyl compounds) to the stereoselective reduction of ketones with borane-tetrahydrofuran, borane-dimethyl sulfide (BMS) or catecholborane.It was named the CBS method (after Corey, Bakshi, and Shibata). Since then, the CBS method has become a standard and has been extensively used, specially for aromatic and a,p-unsaturated ketones, not only in academic laboratories but also in industrial processes. ... 

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