Corey-Bakshi-Shibata reduction

The reduction of ketones by borane catalyzed by chiral oxazaborolidines such as (136), derived from the enantiomeric amino alcohols, has been applied to the synthesis of several drug candidates (127). This system is known as the CBS (Corey, Bakshi, Shibata) reduction (153), and Corey himself has applied it to the synthesis of pharmaceutical compounds (154). A further example is provided by the synthesis of MK-499 (137), a... 

Corey-Bakshi-Shibata reduction Enantioselective reduction of ketones with BH3 using oxazaborolidines as catalysts. 100... 

The Corey-Bakshi-Shibata reduction (CBS reduction) is a highly enantioselective method for arylketones, diaryl ketones, and dialkylketones. In addition, cyclic a,p-unsaturated ketones, acyclic a,p-unsaturated ketones, and a,p-ynones are reduced enantioselectively in a 1,2-fashion. The high enantioselective nature of this reduction relies on the chiral oxazaborolidine catalyst, shown in the reaction scheme, in the presence of borane or a dialkylborane. Reviews (a) Singh, V. K. Synthesis 1992, 605-617. (b) Deloux, L. Srebnik M. Chem. Rev. 1993,93,163-1. (c) Corey, E. J. Helal, C. J. Angew. Chem. Int. Ed. 1998, 37. 1986-2012. 

Scheme 5.7 Fluorous Corey-Bakshi-Shibata reduction of ketones.

Other references related to the Corey-Bakshi-Shibata reduction are cited in the literature. 

The second stereochemical problem, enantioselective reduction of the keto-group in the w-side-chain, was solved by Corey already in 1987. The reduction was successful with borane-THF in presence of 10 mole% of the (H)-prolme-derived (H)-oxazaborolidine (Corey-Bakshi-Shibata reduction). If the enone was reduced in presence of the corresponding (S)-oxazaborolidine, the inverse product distribution resulted. Obviously, the other stereocentres in the educt have no impact on the stereochemical course of the reduction at C-15. 

Cope Elimination Reaction Cope Rearrangement Corey-Bakshi-Shibata Reduction Corev-Kim Oxidation Corey-Winter Olefin Synthesis Comforth Rearrangement Coumarin-Benzofuran Ring Contraction Crafts (see Friedel-Crafts Reaction)... 

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