Oxidation of alkenes and sulphides with a series of hydroperoxides having electron-withdrawing substituents at the α-position

Abstract

The oxidations of alkenes and sulphides with a series of hydroperoxides, α-hydroperoxy-α- methoxyacetophenone (1), α-hydroperoxy-α,α-diphenylacetophenone(2), methyl α-hydroperoxy-α,α- diphenylacetate (3), and α-hydroperoxy-α,α-diphenylacetonitrile (4), were undertaken in a systematic fashion. The data revealed the following. (a) The reactions of electron-rich alkenes (11 a and b) with hydroperoxides (1)–(4) are most likely to proceed by a mechanism similar to that with peracids, as do the oxidations of sulphides (5a–e). (b) For the reaction of less reactive alkenes (11f–k) with hydroperoxide (1) in the presence of oxygen, epoxidation by benzoylperoxyl radical contributes to a significant extent. The reaction with hydroperoxide (2) at 60 °C also seems to proceed by a mechanism involving benzoylperoxyl radical, whereas a molecular epoxidation mechanism is important for the reaction at 30 °C. Perhaps in accord with this, the reaction of 1,1-disubstituted ethylenes (11c–e) with hydroperoxides (1) and (2) results in the formation of considerable amounts of benzoylated products (13) and (14). (c) For the epoxidation with hydroperoxides (3) and (4), however, a molecular epoxidation process seems to predominate. The exceptions the reaction of hydroperoxide (3) with (Z)-2-phenylbut-2-ene and (Z)-stilbene, having very poor reactivity, in which a peroxyl radical, produced by hydrogen abstraction from the hydroperoxide (3), plays an important role in the epoxidation.