Enantioselective catalytic borane reductions of achiral ketones: Syntheses and application of two chiral β-amino alcohols from ( S)-2-indoline carboxylic acid

Abstract

The synthesis of ( S)-α,α-diphenyl-(indolin-2-yl)methanol 1 makes available the chiral oxazaborolidine 2 which is an excellent catalyst for borane reduction of prochiral ketones to chiral secondary alcohols, e.g. acetophenone, in high optical purity The new chiral auxiliary 1 is sythesized from ( S)-2-indoline carboxylic acid in a two step procedure. ( S)-(Indolin-2-yl)methanol 3 is converted to the oxazaborolidine 4 which served also as an enantioselective catalyst in the reduction of aromatic ketones with BH 3·THF.