Enantioselective Borane Reduction of Ketones Catalyzed by a Chiral Oxazaphospholidine Borane Complex

Abstract

Abstract The borane complex of (2R,4S)-2-phenyl-1,3,2- oxazaphospholidine 2 was readily synthetized. This complex can be used as catalyst in enantioselective reduction of ketones in toluene, with BH3:THF (or BH3:SMe2) as reducing agent. The catalytic reduction of iso-propyl methyl ketone yields (R)-3-methyl-2-butanol in 92% e.e. and 100% conversion. Reduction of different ketones under stoichiometric conditions gives the corresponding alcohols in e.e. = 99%.