CATALYTIC ASYMMETRIC EPOXIDATION OF UNFUNCTIONALIZED OLEFINS USING CHIRAL (SALEN)MANGANESE(III) COMPLEXES

Several kinds of chiral (salen)manganese(III) complexes (2 and 3) having chiral salicylaldehyde and chiral ethylenediamine moieties were prepared and used for catalytic asymmetric epoxidation of unfunctionalized olefins with iodosobenzene as a terminal oxidant. Catalysts 2 and 3 were found to show the characteristic substrate specificity for the enantiofacial selection of olefins, respectively. Furthermore, the addition of donor ligands such as pyridine N-oxide or 2-methylimidazole to the epoxidation reaction system was found to alter the enantioselectivity. As a result, the highest enantioselectivity for nonenzaymatic catalytic epoxidation was achieved for (E)-1-phenylpropene (56% ee, with 2c in the presence of 2-methylimidazole), (E)-stilbene (48% ee, with 3a), and dihydronaphthalene (83% ee, with 3a in the presence of pyridine N-oxide).