Synthesis of 2-Arylbenzothiazoles via Condensation of Disulfides with Aldehydes Catalyzed by Na2S under Microwave Irradiation

Background: 2-Substituted benzothiazoles are a class of heterocyclic compounds that have a wide range of applications in agriculture, pharmaceutical and chemical industry due to their wide spectrum of biological and biophysical properties. Benzothiazole is usually prepared by the condensation of 2-aminobenzenethiols or 2,2'-disulfanediyldianilines, the cyclization of thioformanilides, or the sulfurization of 2-haloanilides. Furthermore, in the reaction of 2,2'-disulfanediyldianilines with aldehydes to prepare benzothiazole, the S-S bond cleavage is the key to the construction of C-S bond. Method: 2-Arylbenzothiazoles could be successfully synthesized from the reaction of 2,2'-disulfanediyldianilines with aldehydes by using easily available Na2S·9H2O as a catalyst under microwave irradiation in low power. Results: A novel methodology for preparing 2-arylbenzothiazoles from disulfides and aromatic aldehydes under microwave irradiation in the presence of Na2S has been reported. The reaction mechanism was determined by 1HNMR in detail. It is found for the first time that the S-S bond of the Schiff base could be cleaved by Na2S·9H2O and subsquent could cyclize to form the corresponding 2-arylbenzothiazole. Conclusion: 2-Substituted benzothiazoles were synthesized efficiently via the condensation of 2,2'- disulfanediyldianiline with aromatic aldehydes catalyzed by Na2S·9H2O under microwave irradiation. This methodology provides a green and general synthetic route to prepare benzothiazole with short reaction time, low microwave irradiation power, and high-yield.