(R)-2-Methyl-CBS-oxazaborolidine is an organoboron catalyst that is used in organic synthesis.

This catalyst, developed by Itsuno[1][2] and Elias James Corey,[3][4][5] is generated by heating (R)-(+)-2-(diphenylhydroxymethyl) pyrrolidine along with trimethylboroxine or methylboronic acid.

It is an excellent tool for the synthesis of alcohols in high enantiomeric ratio.

Generally, 2-10 mol% of this catalyst is used along with borane-tetrahydrofuran (THF), borane-dimethylsulfide, borane-N,N-diethylaniline, or diborane as the borane source.

Enantioselective reduction using chiral oxazaborolidine catalysts has been used in the synthesis of commercial drugs such as ezetimibe and aprepitant.