Convenient asymmetric (salen)Mn(III)-catalyzed epoxidation of unfunctionalized alkenes with hydrogen peroxide using carboxylate salt cocatalysts

Asymmetric epoxidation of unfunctionalized alkenes is reported using chiral (salen)Mn(III) complexes 1-5 together with a carboxylate salt cocatalyst in the presence of either aqueous H2O2 or anhydrous urea-H2O2 adduct as oxidant. Several simple soluble salts (acetates, formates, benzoates) were studied all giving good yields of epoxides with moderate to excellent enantioselectivity. For example, 1,1-diphenyl-1-propene was converted into the corresponding epoxide of 96% ee in 84% yield. Generally, this epoxidation method gave better results than a previously described system using nitrogen heterocycles as cocatalysts. (C) 1998 Elsevier Science Ltd. All rights reserved.