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Under neutral conditions cis sulfoxides 5 underwent a sigmatropic rearrangement with 2-methylene hydrogens to give sulfenic acids 18, followed by Cyclization to dihydro-1,4-dithiins 2. The trans sulfoxides 6 rearranged involving 2-methyl hydrogens to form isomeric dihydrodithiins 3 via sulfenic acids 19. In the reactions of both the sulfoxides, sulfides 4 and disulfides 11 were also formed as minor side products. In the presence of acid catalyst cis sulfoxides 5 produced 2 in quantitative yields while the trans sulfoxides 6 gave a mixture of 2 and 3. The mechanism of formation of 2,3,4 and 11 are discribed.

Two methods for constructing dihydro-1,4-thiazine 4 were described. 1,3-Thiazolidines 5 were converted to dihydro-1,4-thiazines 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 1,3-thiazolidine 1-oxyde 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 3-bromo-2-oxobutanoic acid derivatives

Synthese de derives des acides dihydro-5,6 methyl-2 oxathiinne-1,4carboxylique-3 et dihydro-5,6 oxathiinne-1,4acetique-2 a partir respectivement des S-oxydes de derives d'acides cis- et trans-methyl-2 oxathiolanne-1,3acetiques-2