Mechanism of oxidative ring closure of compounds of the buta-1,3-diene-1-thiol type with halogens to give thiophen derivatives

Abstract

The mechanism of oxidative ring closure of compounds of the above type to thiophen derivatives has been studied in detail. It is suggested that in aprotic solvents a sulphenyl halide is formed, rather than the disulphide postulated by Campaigne and Cline, as a reactive intermediate, which then cyclises to the thiophen derivative, probably by a polar mechanism. A free-radical mechanism is not, however, completely ruled out, and is indeed proposed for the cyclisation under other reaction conditions.