Asymmetric Reduction of Ketones with Sodium Borohydride in the Presence of Phase Transfer Catalysts

Asymmetric reduction of various ketones with sodium borohydride in the presence of chiral onium salts in two phase system afforded the corresponding alcohols with 0–43% e. e. The extent of asymmetric synthesis and the configuration of the predominant enantiomer were dependent on the structure of both substrate and catalyst.