Thionation of N-methyl- and N-unsubstituted thiazolidine enaminones

The potential of directional non-bonded 1,5-type (SO)-O-... interactions to initiate the incipient stage of an in situ rearrangement of N-unsubstituted thiazolidine enaminones to functionalized 1,2-dithioles has been demonstrated. The spectral characteristics, as well as X-ray structural analysis of a selected rearranged product, indicate that a dynamic interconversion occurs in solution between the 1,2-dithiole and the 3,3alambda(4),4-trithia-1-azapentalene bicylic form. The lack of the rearrangement in the case of a N-methyl Substituted enaminone precursor is attributed to an unfavorable methyl migration in the last reaction step.