Conversion of 1,3­thiazolidine and its sulfoxide to dihydro­1,4­thiazine

Abstract

Two methods for constructing dihydro­1,4­thiazine 4 were described. 1,3­Thiazolidines 5 were converted to dihydro­1,4­thiazines 4 by chlorinolysis through the unisolable chlorosulfonium salt 10 and sulfenyl chloride 11. Oxidation of the sulfides 5 gave a mixture of pairs of diasteromers 6. In the presence of acid catalyst, both sulfoxides were converted to dihydrothiazine 4 through sulfenic acid 22. In this reaction the stepwise ring opening involving carbocation 23 seems more probable. The structures of 4 were proven by the independent synthesis involving 3­bromo­2­oxobutanoic acid derivatives. Copyright ？ 1993 Journal of Heterocyclic Chemistry