Highly Selective Epoxidation of Cycloaliphatic Alkenes with Aqueous Hydrogen Peroxide Catalyzed by [PO4{WO(O2)2}4]3−/Imidazole

Abstract In the presence of imidazole as an additive, a phosphorus‐containing tetranuclear peroxotungstate, THA 3 [PO 4 {WO(O 2 ) 2 } 4 ] ( I , THA=tetra‐ n ‐hexylammonium), could act as an efficient catalyst for epoxidation of cycloaliphatic alkenes with 30 % aqueous hydrogen peroxide (H 2 O 2 ). Compound I showed higher catalytic activity and selectivity to epoxide than other tungstates. By using the I /imidazole system, various kinds of cycloaliphatic alkenes could be highly selectively converted into the acid‐sensitive epoxides including industrially important diepoxides in high to excellent yields under the almost stoichiometric conditions. The 1 H NMR spectroscopy showed that imidazole would work not only as a proton acceptor but also as a Lewis base to remarkably suppress the acid‐catalyzed ring opening of epoxides.