NEW ROUTES TO BENZOTHIOPHENES, ISOTHIAZOLES AND 1,2,3-DITHIAZOLES

4,5-Dichloro-1,2,3-dithiazolium chloride 1 condenses with active methy lene compounds, such as malononitrile, barbituric acid and Meldrum's a cid, to give the dithiazol-5-ylidene derivatives, such as 3, 4 and 5, in modest yields. Better yields are obtained from 4-chloro-1,2,3-dithi azole-5-thione 6. Thus the thione 6 condenses with diphenyldiazomethan e in a very mild version of the Barton double extrusion synthesis of h indered alkenes; this requires neither heat to extrude nitrogen nor a phosphine to abstract sulfur, to give the alkene 7 (83%) (Scheme 1). T his alkene rearranges at room temperature, with loss of hydrogen chlor ide and sulfur, to give the benzothiophene 13 (89%) in a new thiophene ring-forming reaction (Scheme 2). The thione 6 also condenses with te tracyanoethylene oxide to give a better yield of the dicyanomethylene compound 3 (70%) (Scheme 4). Compound 3, in turn, reacts with morpholi ne and with chloride ions (Scheme 5) to give 3-morpholino-19 (60%) and 3-chloro- 20 (100%) isothiazole-4,5-dicarbonitrile, in a new isothiaz ole ring synthesis. Mechanisms are proposed for all of these reactions .