Enantioselective Borohydride Reduction Catalyzed by Optically Active Cobalt Complexes

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 β‐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. Optically active cobalt complexes catalyzed the highly enantioselective borohydride reduction of aromatic ketones or imines to the corresponding alcohols and amines. Using a precisely premodified borohydride with different alcohols such as tetrahydrofurfuryl alcohol, ethanol and methanol, high enantioselectivities were realized by choosing a suitable β‐ketoiminato ligand of the catalyst such as depicted. This reaction was 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.