Design and Synthesis of Optically Active Manganese(III) Complex Catalysts for Enantioselective Epoxidation Using Molecular Oxygen

Epoxidation of olefins by molecular oxygen was developed by combining aldehyde with a catalytic amount of nickel (II), iron (III), vanadium (IV), and manganese (II) complexes containing 1,3-diketona-to ligands. The efficiency of catalysts was improved by designing the structure of the ligands, and various olefins, styrene derivatives, and α,β -unsaturated carboxamides were oxidized to the corresponding epoxides in high yields. It was also revealed that the stereofacial selection of cholesteryl derivatives in the aerobic epoxidation was different from that of the conventional epoxidation using peroxy acids, such as mCPBA or peracetic acid. Novel manganese (III) complexes having optically active 1,3-diketo-type ligands, N, N-bis (3-oxobutylidene) diamine derivatives, were designed and synthesized on the basis of the characterization of X-ray analysis. In the presence of a catalytic amount of these manganese (III) complexes, enantioselective and aerobic epoxidations of unfunctionalized olefins were achieved by the combined use of molecular oxygen and pivalaldehyde, and the corresponding optically active epoxides were obtained with good-to-high enantiomeric excess. It was found that the absolute configuration of the resulting epoxides was reversed by the addition of N-methyUmidazole. Based on these observations, the key intermediates in the present aerobic epoxidation were tentatively proposed to be acylperoxo-manganese complexes.