Single and double asymmetric inductions were achieved by the sodium borohydride reduction of α-ketoesters in the presence of chiral phase transfer catalysts. The quaternary ammonium salts with hydroxyl group in the substituent moiety showed the effective catalytic activity. The reduction of (-)-(3R)-menthyl benzoylformate gave (3R)-menthyl (S)-mandelate in contrast to the prediction by the Prelog rule.
