New routes to benzothiophenes, isothiazoles and 1,2,3-dithiazoles

Kumaraswamy Emayan, Russell F. English, Panayiotis A. Koutentis, Charles W. Rees
1997 Journal of the Chemical Society, Perkin Transactions 1: Organic and Bio-organic Chemistry  
4,5-Dichloro-1,2,3-dithiazolium chloride 1 condenses with active methylene compounds, such as malononitrile, barbituric acid and Meldrum's acid, 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-dithiazole-5-thione 6. Thus the thione 6 condenses with diphenyldiazomethane in a very mild version of the Barton double extrusion synthesis of hindered alkenes; this requires neither heat to extrude nitrogen nor a phosphine
more » ... gen nor a phosphine to abstract sulfur, to give the alkene 7 (83%) (Scheme 1). This alkene rearranges at room temperature, with loss of hydrogen chloride and sulfur, to give the benzothiophene 13 (89%) in a new thiophene ring-forming reaction (Scheme 2). The thione 6 also condenses with tetracyanoethylene oxide to give a better yield of the dicyanomethylene compound 3 (70%) (Scheme 4). Compound 3, in turn, reacts with morpholine and with chloride ions (Scheme 5) to give 3-morpholino-19 (60%) and 3-chloro-20 (100%) isothiazole-4,5dicarbonitrile, in a new isothiazole ring synthesis. Mechanisms are proposed for all of these reactions.
doi:10.1039/a704916a fatcat:dgtpacmyvjbl5mzinydnczuzbi