The highly enantioselective borohydride reduction of aromatic ketones or imines to the corresponding alcohols was developed in the presence of a catalytic amount of an optically active cobalt(II) complex catalyst. This enantioselective reduction is carried out using a precisely premodified borohydride with alcohols such as tetrahydrofurfuryl alcohol, ethanol and methanol. High optical yields are obtained by choosing the appropriate alcohol as modifiers and a suitable beta-ketoiminato ligand of the catalyst. The enantioselective borohydride reduction has been successfully applied to the preparation of optically active 1,3-diols, the stereoselective reduction of diacylferrocenes, and dynamic and/or kinetic resolution of 1,3-dicarbonyl compounds.

The enantioselective borohydride reduction using optically active cobalt(II) complex catalysts was successfully applied to various aryl N-diphenylphosphinyl imines, and the corresponding reduced products were obtained in good yields with high enantiomeric excesses (up to 99% ee). The optically active primary amines were obtained by the successive hydrolysis under mild conditions.

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