Formation of thiazole and 1,3-thiazolidine sulfoxide from pyrolysis of a thiolsulfinate

The mechanistic study on the pyrolytic transformation of a thiolsulfinate (2) is described. The reactive intermediates sulfenic acid (6) and thioaldehyde (8) were formed resulting from S-S bond cleavage and a hydrogen transfer from sulfenyl to sulfinyl moiety. A stereospecific cyclization of 6 to cis-sulfoxide (4) was observed, which arouse from the geometrical requirements of a planar transition state for the reacting bonds and atoms in the sigmatropic rearrangement. In the transformation of 8 to thiazole (9), the amide carbonyl group facilitated the elimination of a neighboring proton and enabled to furnish the nucleophilic attack of a thiocarbonyl sulfur at beta to internal carbonyl group to yield thiazole (9).