Synthesis of benzothiazole from 2-aminothiophenol and benzaldehyde catalyzed by alkyl carbonic acid

A simple and green method was developed for the reaction of 2-aminothiophenol and benzaldehyde in the self-neutralizing acidic CO2-alcohol system to produce benzothiazoles. A series of benzothiazole derivatives were successfully prepared from the condensation and cyclization reaction of 2-aminothiophenol or substituted 2-aminothiophenol with aliphatic, heteroaryl and aryl aldehydes promoted by alkyl carbonic acid under mild conditions. Moreover, the method is also suitable for the synthesis of 2-phenylbenzimidazole and 2-phenylbenzoxazole. Additionally, this reaction system greatly simplified post-processing, which did not need to be neutralized with base and without salt disposal. These advantages make the process more practical, economical, and environmentally friendly. Mechanism investigation indicated that formation of alkyl carbonic acid from CO2 and methanol is the key intermediate, which provides hydrogen ions to catalyze the reaction of 2-aminothiophenol and benzaldehyde.