Catalytic asymmetric epoxidation of stilbene using a chiral salen complex immobilized in Mn-exchanged Al-MCM-41

Manganese-exchanged Al-MCM-41 modified by the chiral salen ligand [(R,R)-(−)-N,N′-bis(3,5-di-tert-butylsalicylidene)cyclohexane-1,2-diamine] can be used as an enantioselective heterogeneous epoxidation catalyst using iodosyl benzene as oxygen donor. Epoxidation of (Z)- and (E)-stilbene is studied in detail and experiments are described that demonstrate that the reaction is wholly catalysed heterogeneously. Similar enantioselectivity is observed for the oxidation of (Z)-stilbene to the (E)-epoxide using homogeneous (77.5% ee) or heterogeneous (70% ee) catalysts. The effect of temperature, solvents and donor ligands on the yield and enantioselection are discussed.