Highly enantioselective borane reduction of prochiral ketones catalyzed by C₃-symmetric tripodal β-hydroxy amides

The asymmetric borane reduction of prochiral ketones with a series of easily constructed chiral C₃-symmetric tripodal tris(β- hydroxyamide) ligands was investigated. The borane complex of chiral ligand 1,1′,″,-(1,3,5-benzenetricarbonyl)-tris[(2S)-α, α-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).