Enantioselective epoxidation of electrophilic olefins by using glycosyl hydroperoxides.
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.
Kośnik
Wioletta
W
Institute of Organic Chemistry of the Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
Bocian
Wojciech
W
Kozerski
Lech
L
Tvaroska
Igor
I
Chmielewski
Marek
M