Dramatic Change of Carbonyl Oxide Reactivity by the Potent Electron-Withdrawing Trifluoromethyl Group.

Abstract

alpha,alpha,alpha-Trifluoroacetophenone oxide, generated by (1)O(2) oxidation of Ph(CF(3))CN(2), reacted electrophilically with sulfoxides (rho = -0.74 vs sigma; r = 0.95) affording sulfides as the major product. The intermediacy of persulfoxides formed via cyclic peroxidic sulfuranes in the novel deoxygenation was evidenced by an (18)O-tracer study and by the formation of benzaldehyde in the reaction with benzyl phenyl sulfoxide. Olefins were oxidized to epoxides during the photooxidation of Ph(CF(3))CN(2). From the fact that the epoxidation proceeded almost stereospecifically and the substituent effect on styrenes resulted in the negative rho-value of -1.66 vs sigma (r = 0.97), a dioxirane was proposed as the second intermediate which might be formed by the isomerization of carbonyl oxide. Trapping experiments with styrenes and sulfoxides suggested that the cyclization of carbonyl oxide is competitive with the reaction with sulfoxides. In contrast to the known nucleophilic nature of carbonyl oxides, the present oxide is shown to have an electrophilic character, indicating that the reactivity of carbonyl oxides could be controlled by substituents.