Studies of heterocyclic compounds. Part III. A synthesis of 4H-indeno[2,1-d]thiazolium salts

N-Substituted thioamides react with 1-bromoindan-2-one to give thiolimidate ester salts which are cyclised to 4H-indeno[2,1-d]thiazolium salts by thionyl chloride in dimethylformamide or phosphorus pentachloride in nitromethane. Primary thioamides lead to 4H-indeno[2,1-d]thiazoles.