Asymmetric Epoxidation of Unfunctionalized Alkenes with Ammonium and Phosphonium Monopersulfates Catalyzed by Chiral Mn(III)–Salen Complexes

Simple cis-disubstituted and trisubstituted alkenes were enantioselectively epoxidized in mild conditions using various Mn(III)–salen complexes as catalysts and quaternary ammonium and phosphonium monopersulfates (Bu4NHSO5, Ph4PHSO5) as oxidants together with amine N-oxides as additives. The effect of the catalyst structure on the stereochemical outcome of the epoxidation reactions was studied. Generally, the 1,2-diphenylethylenediamine-derived complexes were found to give higher asymmetric induction compared to their 1,2-diaminocyclohexane-derived counterparts. Particularly high yields of epoxides (up to 98%) and good enantiomeric excesses (ee up to 93%) were obtained in the epoxidation of 2,2-dialkylchromenes and trisubstituted alkenes.