Thienoisothiazoles. I. The synthesis of Thieno[2,3-c]isothiazole and some of its derivatives

.Thieno[2,3-c]isothiazole-3-carboxylic acid was the compound obtained by the reaction of ethyl-3-cyano-5,5-diethoxy-2-oxopentanoate with phosphorus pentasulfide, previously assumed to yield thieno[3,4-d]isothiazole-4-carboxylic acid. The parent thieno[2,3-c]isothiazole was obtained by decarboxylation of thieno[2,3-c]isothiazole-3-carboxylic acid and by deamination of thieno[2,3-c]-isothiazol-3-amine.