Chiral Mn(III) salen complex-catalyzed enantioselective epoxidation of nonfunctionalized alkenes using urea_H_2O_2 adduct as oxidant

摘要

Enantioselective epoxidation of chromenes indene and styrene mediated by manganese salen complexes 1a-b,2a-b (1 mol%) as catalysts with urea-H_2O_2 adduct as an oxidant is observed to give excellent epoxide yield (>99%) in 0.5-4 with enantiomeric excess (ee) in the reange 56-99% except for styrene in which case 23-39% ee was obtained in 20 h Even with a catalyst loading of 0.4 mol% the system works efficiently with retention of enantioselectivity albeit with an increase in reaction time Kinetic investigations of a representative substrate indene with these catalysts indicated a kninetic profile having first-order dependence with respect to the concentrations of the catalyst and oxidant and indepencdent of-initial concentration of the substrate Based on kinetic catalytic and experimental evidence the mechanism of the epoxidatin reaction is suggested.