Enantioselective borohydride reduction of ketones catalyzed by optically active cobalt(II) complexes: Achievement of high enantioselection by modified borohydrides with furfuryl alcohol derivatives

The enantioselective borohydride reduction of ketones catalyzed by optically active (β-oxoaldiminato) cobalt(II) complexes was remarkably improved by using the borohydride which was modified with furfuryl alcohol derivatives and ethanol. In the presence of 1 mol% of the above complex catalysts, asymmetric reduction of aromatic ketones proceeded smoothly to give the corresponding optically active alcohols in quantitative yields within 6-12 h with high enantiomeric excesses (90-97% ee).