Unfunctionalized aromatic alkenes were enantioselectively epoxidized with peroxycarboxylic acids prepared in situ from urea-H2O land other anhydrous adducts of H2O2) and carboxylic acid anhydrides (maleic, phthalic, and acetic anhydride) using chiral Mn(III)-salen complexes as catalysts and N-methylmorpholine N-oxide (NMO) as an additive. Experimental results were compared with those reported earlier that employed aqueous hydrogen peroxide as the primary oxidant and the method presented here was found to offer both higher enantioselectivities and shorter reaction times. This novel epoxidation system was also compared with the Jacobsen's MCPBA/NMO system, and some differences in reactivity and selectivity were observed. These differences could possibly be explained assuming the presence of alternative mechanistic pathways during the catalytic cycle of the asymmetric epoxidation.