Corey-Bakshi-Shibata reduction

eWhat is Corey-Bakshi-Shibata reduction?

The Corey-Bakshi-Shibata reduction, also known as the CBS reduction, is an enantioselective reduction of ketones using borane, catalyzed by chiral oxazaborolidines. This reduction was first reported in 1987 by Corey and co-workers, and is known for its exceptional enantioselectivity, high chemical yield, and turnover of the catalyst.

Corey-Bakshi-Shibata reduction - Corey-Itsuno reduction
Corey-Bakshi-Shibata reduction

R1 < R2 , R3 = H, Me

The endocyclic boron-methylated catalyst, also known as the Corey-Bakshi-Shibata catalyst or CBS catalyst, has superior air and moisture stability and functions through a catalytic cycle in four steps: nitrogen atom coordination to borane, complexation of the ketone to the endocyclic boron as a Lewis acid, hydride transfer from borane to the carbonyl carbon, and dissociation of the alkoxyborane moiety to regenerate the catalyst.