The enantioselective reduction of ketones using borane and a chiral oxazaborolidine as catalyst (CBS catalyst). Usually, MeCBS is used (R'' = Me, but selectivity may be increased by varying this substituent).
Mechanism of the Corey-Bakshi-Shibata Reduction
The mechanism depicted (E. J. Corey, C. J. Helal, Angew. Chem. Int. Ed., 1998, 37, 1986-2012. DOI) portrays the rationale for the enantioselectivity and high reaction rates, which are influenced only by the CBS catalyst. This catalyst is a combination of both a Lewis acid and a chiral auxiliary!
Practical enantioselective reduction of ketones using oxazaborolidine catalyst generated in situ from chiral lactam alcohol and borane
Y. Kawanami, S. Murao, T. Ohga, N. Kobayashi, Tetrahedron, 2003, 59, 8411-8414.
A novel enantioselective synthesis of α-amino acids has been developed, which is broad in scope, simple in application, and advantageous for many α-amino acids of interest in chemistry, biology, medicine.
E. J. Corey, J. O. Link, J. Am. Chem. Soc., 1992, 114, 1906-1908.