Highly Enantioselective Borane Reduction of Prochiral Ketones Catalyzed by C3-Symmetric Tripodal (beta)-Hydroxy Amides

The asymmetric borane reduction of prochiral ketones with a series of easily constructed chiral C3-symmetric tripodal tris(?hydroxyamide) ligands was investigated. The borane complex of chiral ligand 1,1ʹ,1"-(1,3,5-benzenetricarbonyl)-tris[(2S)-(alpha),(alpha)diphenyl-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).