Catalytic and asymmetric epoxidation of unfunctionalized alkenes with hydrogen peroxide and (Salen)Mn(III) complexes

Abstract

Catalytic epoxidation of two unfunctionalized alkenes, 1,2-dihydronaphthalene and trans-β-methylstyrene, is reported using achiral and chiral (Salen)Mn(III) complexes 1– 3 together with a nitrogen heterocycle as axial ligand in the presence of 30 % aqueous hydrogen peroxide as oxidant. Typically, the reaction system consisted of the substrate, oxidant, ligand, and salen in a ratio of 1: 2–3.5: 0.4: 0.025–0.05. The best ligands were imidazole and N-methyl imidazole. The highest ee-values obtained were 60 % for 1,2-dihydronaphthalene oxide and 47 % for trans-β-methylstyrene oxide.