Enantioselective Carbonyl-Ene Reaction of Glyoxal Derivatives Catalyzed by Cationic 3-Oxobutylideneaminatocobalt(III) Complexes

Optically active 3-oxobutylideneaminatocobalt(III) complexes were designed for the catalytic enantioselective carbonyl-ene reaction. Varieties of counter anions of cationic cobalt(III) complexes were screened and hexafluoroantimonate was found to be the most effective. In the presence of cobalt(III) hexafluoroantimonate complex 1f, the enantioselective carbonyl-ene reaction of various alkenes with glyoxal derivatives was carried out to afford the corresponding homoallylic alcohols in high yields and with high enantioselectivities. Even in the presence of 0.2 mol% cobalt(III) complexes, the reaction proceeded in high yield and with maintained high enantioselectivity. The absolute configuration of the optically active product was determined and a reasonable explanation for the enantioselection in the present carbonyl-ene reaction catalyzed by the cobalt complex was proposed.