A novel transformation of 1,2-dithiole-3-thiones into 1,3-thiazine-4- thiones

1,2 Dithiole 3 thiones 1 exhibit a variety of reactivi ties.1 1,3 Dipolar cycloaddition of these compounds is best studied: the reaction involves ring opening with participation of the thione group. Transformations with retention of the thione group are much more uncommon. 1,2 Dithiole 3 thiones have been reported to react with α,β unsaturated nitriles to give thiopyran thiones2 and with amines to give 1,2 thiazole 3 thiones or 1,2 isothiazole 5 thiones.3 We discovered a novel transformation of the dithiole ring. In reactions of 1,2 dithiole 3 thiones 1a—d with 3,4 dihydropyrrolo[1,2 a]pyrazine (2), the imine frag ment of compound 2 is inserted into the 1,2 dithiole ring with extrusion of the S atom (the latter was isolated as elemental sulfur in a nearly quantitative yield) to give fused 1,3 thiazine 4 thiones 3a—d in high yields (Scheme 1). The transformation is possible for both fused (1a—c) and monocyclic 1,2 dithioles (1d). Such reactions in volving the insertion of nitrogen containing fragments into the 1,2 dithiole ring give wide scope for the synthesis of novel heterocyclic systems. The structures of 1,4 thiazine 4 thiones 3a—d were fully confirmed by elemental analysis data and 1H and 13C NMR, IR, and mass spectra. Some of the spectral Scheme 1