Chemical Synthesis

CBS Catalysts

2-Methyl-CBS-oxazaborolidines for asymmetric reduction

Since 1987, the series of chiral oxazoborolidines known as CBS catalysts (after the work of Corey, Bakshi, and Shibata) have been used for catalytic reduction of prochiral ketones¹, imines², and oximes³ to produce chiral alcohols, amines, and amino alcohols in excellent yields and ee’s. Sigma-Aldrich is pleased to offer both enatiomers of 2-methyl-CBS-oxazaborolidine as a dry reagent, in addition to our current offerings as a 1M solution in toluene.

Product Name Product # 
(R)-2-Methyl-CBS-oxazaborolidine 649317
(S)-2-Methyl-CBS-oxazaborolidine 649309
(R)-2-Methyl-CBS-oxazaborolidine, 1M solution in toluene 457698
(S)-2-Methyl-CBS-oxazaborolidine, 1M solution in toluene 457701

o-Tolyl-CBS-oxazaborolidines for asymmetric synthesis

We are also pleased to offer the o-tolyl-CBS-oxazaborolidine as a 0.5M solution in toluene for your research needs. When protonated with trifluoromethanesulfonimide (product # 46463-5), these chiral oxazaborolidines generate chiral Lewis acids which have demonstrated great utility in the enantioselective Diels-Alder reaction (Scheme 1).4

Product Name Product # 
(R)-o-Tolyl-CBS-oxazaborolidine, 0.5M in toluene 654299
(S)-o-Tolyl-CBS-oxazaborolidine, 0.5M in toluene 654302


  1. (a) Corey, E. J.; Bakshi, R. K.; Shibata, S. J. Am. Chem. Soc. 1987, 109, 5551;
    (b) Corey, E. J. et al. ,J. Am. Chem. Soc.1987, 109, 7925.
  2. (a) Kirton, E. H. M. et al. Tetrahedron Lett. 2004, 45, 853;
    (b) Cho, B. T.; Chun, Y. S. Tetrahedron: Asymmetry 1992, 3, 337;
    (c) Cho, B. T.; Chun, Y. S. J. Chem. Soc., Perkin Trans. 1 1990.
  3. Tillyer, R. D. et al. Tetrahedron Lett. 1995, 36, 4337.
  4. Ryu, D. H. and Corey, E. J. J. Am. Chem. Soc. 2003, 125, 6388.