Novel synthesis of thieno[2,3-d] and 1,2-dithiino[4,5-c] Thiazoles

Thionation of 3-substituted-5-(2-aryl-2-oxoethyl)-2-thioxo-4-oxo-1,3-thiazolidines 1a-e either with tetraphosphorous decasulfide or with Lawesson's reagent in xylene affords the respective 3-substituted-5-aryl-2,3-dihydro [2,3-d] 1,3-thiazole-2-thiones 2a-e . However, thionation of 1f affords 3-(3-methylphenyl)-6-(4-ethylphenyl)-2-thio-2,3-dihydrothiazolo[4,5-c]1,2-dithin 3 . The structure of the synthesized compounds were supported by microanalytical and spectral evidence. A rationalization for the route of conversion was also given.