Oxidation of benzotrithiole analogues. Photochemical rearrangement of benzotrithiole 2-oxides to benzotrithiole 1-oxides involving intramolecular oxygen migration

Abstract

4,8-Dialkylbenzo[1,2-d;4,5-d′]bis[1,2,3]trithioles 2 were readily oxidized by m-chloroperbenzoic acid, N-bromosuccinimide and N-iodosuccinimide to form both benzobistrithiole 1 - and 2-oxides (4 and 5), and the ratio was dramatically affected by the kind of oxidizing agent used. Irradiation of the oxidized produts, benzobistrithiole 2-oxides 5, in acetonitrile with a high-pressure mercury lamp gave benzobistrithiole 1 -oxides 4 quantitatively. Photolysis of benzo- and naphtho-trithiole 2-oxides also yielded benzo- and naphtho-trithiole 1 -oxides. These photochemical oxygen migrations were shown to proceed intramolecularly via an excited singlet state by ¹⁸O-labelled, cross-over and triplet quencher experiments.