Catalyst-free reductive cyclization of bis(2-aminophenyl) disulfide with CO(2) in the presence of BH(3)NH(3) to synthesize 2-unsubstituted benzothiazole derivatives

An efficient and catalyst-free methodology for the reductive cyclization of various disulfides using BH(3)NH(3) as a reductant and CO(2) as a C1 resource was developed. The desired 2-unsubstituted benzothiazole derivatives were obtained in good to excellent yields. Moreover, mechanism investigation demonstrated that BH(3)NH(3) played an important role in the formation of benzothiazole. As a reducing agent, BH(3)NH(3) reduced CO(2) and cleaved the S–S bond of the disulfide efficiently. In addition, the N–H bond of the amino group was also activated by BH(3)NH(3). To the best of our knowledge, this is an unprecedented catalyst-free protocol for the synthesis of 2-unsubstituted benzothiazole from bis(2-aminophenyl) disulfide and CO(2).