Scandium-Catalyzed Ring-Opening Desymmetrization of meso-Epoxides

Abstract

In the presence of catalytic amounts of Sc(DS) 3 and chiral bipyridine ligand 1, ring-opening desymmetrization of meso-epoxides with aromatic amines and indole derivatives proceeded smoothly in water without using any organic solvents to afford the corresponding adducts in high yields with high enatioselectivities.Interestingly, the Sc-caytalyzed reactions proceeded much faster in water than in dichloromethane. INTRODUCTIOMNThe ring-opening desymmetrization of meso-epoxides with nucleophiles provides an efficient and powerful strategy for constructing two contiguous stereogenic centers in a single event.The reactions proceed under Lewis acidic conditions in most cases, and combinations of chiral Lewis acids and nucleophiles have been investigated. 1 On the other hand, organic reactions in water are now of great interest because water is an inexpensive, safe, and clean solvent, and unique reactivity and selectivity are often observed by using water as a solvent. 2 After discovery of water-compatible Lewis acids, 3 we have searched for chiral Lewis acids that work efficiently in aqueous media, 4 and recently a novel chiral scandium complex prepared from Sc(OTf) 3 and chiral bipyridine 1 5 has been found to catalyze enantioselective hydroxymethylation reactions of silicon enolates using an aqueous formaldehyde solution (HCHO aq.). 6While efficient chiral Lewis acid catalysis in aqueous media has been attained based on Sc for the first time, a certain amount of an organic co-solvent combined with water was needed HETEROCYCLES, Vol.72, 2007