Asymmetric Ring-Opening Reactions of meso-Epoxides Using Metal-Chiral Bipyridine Complexes

The chiral bipyridine ligand developed by C. Bolm in 1990 has been revived after 15 years. In this review article, the ring-opening reactions of meso-epoxides with several nucleophiles such as aniline derivatives, alcohols, thiols, indoles, etc. using metal-chiral bipyridine complexes as catalysts are surveyed. Remarkably, the reactions proceeded smoothly in water. For example, in the presence of Sc(III), Zn(II) and Cu(II) surfactant-type catalysts, the ring-opening reactions proceeded smoothly in water to afford the corresponding products in moderate to high yields with good to excellent enantioselectivities. Opposite enantiomers were obtained by using Sc(III) and Zn(II) or Cu(II) with the same chiral bipyridine ligand. Crystal structures of these catalysts may explain the reversal of the enantioselectivity. Some reactions were also tested in dichloromethane (DCM), and it was revealed that the reactions proceeded faster in water than in DCM. Bi(III) and In(III)-chiral bipyridine complexes as chiral catalysts are also discussed.