Enantioselective epoxidation of electrophilic olefins by using glycosyl hydroperoxides

Article abstract of DOI:10.1002/chem.200800051

Anomeric hydroperoxides derived from 3,4,6-tri-O-benzyl-galactose and glucose were used for enantioselective epoxidation of naphthoquinone (12), chalcone (13), (E)-1,2-dibenzoyl ethylene (14) and (E)-iso-butyryl-phenyl ethylene (15). In the presence of sodium hydroxide, the epoxidations showed exceptional high asymmetric induction. The exchange of sodium by a potassium ion resulted in a low asymmetric induction. These results pointed to the crucial role of the counterion and strongly suggested that coordination of the alkaline ion occurs in the transition state of the epoxidation process by both reagents, hydroperoxide and the olefin. Theoretical studies of the reaction mechanism at the DFT B3LYP/6-31G* level fitted very well with experimental results.