CONVERSION OF 1,3-THIAZOLIDINE AND ITS SULFOXIDE TO DIHYDRO-1,4-THIAZINE

Two methods for constructing dihydro-1,4-thiazine 4 were described. 1, 3-Thiazolidines 5 were converted to dihydro-1,4-thiazines 4 by chlorin olysis through the unisolable chlorosulfonium salt 10 and sulfenyl chl oride 11. Oxidation of the sulfides 5 gave a mixture of pairs of diast eromers 6. In the presence of acid catalyst, both sulfoxides were conv erted 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 involvi ng 3-bromo-2-oxobutanoic acid derivatives.