Highly Enantioselective Borane Reduction of Prochiral Ketones Catalyzed by C3-Symmetric Tripodal β-Hydroxy Amides

Abstract

The asymmetric borane reduction of prochiral ketones with a series of easily constructed chiral C-3-symmetric tripodal tris(beta-hydroxyamide) ligands was investigated. The borane complex of chiral ligand 1,1',1-(1,3,5-benzenetricarbonyl)-tris[(2S)-alpha,alpha-diphenl-2-pyrrolidinemethanol] (1h) was found to be an efficient catalyst in asymmetric borane reduction of prochiral ketones and excellent enantioselectivities were obtained with both electron-deficient and electron-rich prochiral ketones (up to 97% ee).