Synthesis of 1,1-dialkylindolium-2-thiolates via base-induced transformation of 4-(2-chloro-5-nitrophenyl)-1,2,3-thiadiazole in the presence of secondary amines

4-(2-Chloro-5-nitrophenyl)-1,2,3-thiadiazole undergoes ring-opening to produce a thioketene intermediate that reacts with secondary amines forming 2-(2-chloro-5-nitrophenyl)-N,N-dialkylthioacetamides. Intramolecular cyclization of these thioamides via nucleophilic substitution of the halogen on the aromatic ring affords nonaromatic 1,1-dialkylindolium-2-thiolates instead of the expected aromatic N,N-dialkylaminobenzob]thiophenes.