Taketo Ikeno

Manganese and cobalt 3-oxobutylideneaminato complexes: Design and application for enantioselective reactions

Abstract The optically active 3-oxobutylideneaminato transition-metal complexes have been developed as efficient catalysts for a variety of enantioselective reactions; e.g. the corresponding manganese(III) complexes catalyzed the enantioselective aerobic epoxidation of unfunctionalized olefins, and the corresponding cobalt complexes have been developed for the enantioselective borohydride reduction of various carbonyl compounds. The cobalt complexes could also be employed for the catalytic enantioselective cyclopropanation with diazoacetates and the Lewis acid catalyses such as the hetero Diels–Alder reaction, carbonyl–ene reaction, and 1,3-dipolar cycloaddition of nitrones. In the presence of the cobalt complex, the Henry reaction proceeded with a high enantioselectivity, and the enantioselective chemical fixation of carbon dioxide to obtain the optically active cyclic carbonate. In these Lewis acid catalyses, the valence of cobalt and the counter anion have significant effects on the reaction rate and stereoselectivity.

Endo-Selective Asymmetric Inverse Electron-Demand 1,3-Dipolar Cycloaddition Reaction of Nitrones

In the presence of a catalytic amount of the optically active cobalt(III) hexafluoroantimonate, the inverse electron-demand 1,3-dipolar cycloaddition reaction of dihydrofuran with nitrones bearing an electron-withdrawing group effectively proceeded to afford the corresponding adducts with excellent endo-selectivity.