The reaction of 4,5-dichloro-1,2,3-dithiazolium chloride with dimethylsulfonium dicyanomethylide: an improved synthesis of (4-chloro-1,2,3-dithiazolylidene)malononitrile

4,5-Dichloro-1,2,3-dithiazolium chloride 6 (Appel salt) reacts with dimethylsulfonium dicyanomethylide 11 to give 5-(4-chloro-1,2,3-dithiazolylidene)malononitrile 1 and a mixture of E/Z isomers of 3-(4-chloro-5H-1,2,3-dithiazol-5-ylideneamino)-3-chloro-2-(methylthio)acrylonitrile 13. The reaction of 4-chloro-5H-1,2,3-dithiazole-5-thione 10 with dimethylsulfonium dicyanomethylide 11 gives (dithiazolylidene)malononitrile 1 in 92% yield. All new compounds are fully characterised and rational mechanisms are proposed for the formation of all key compounds.