Highly Efficient and Selective Electrochemical Synthesis of Substituted Benzothiophenes and Benzofurans in Microcontinuous Flow
Dong Zhang, Jinlin Cai, Zheng Fang, Jinze Du, Xinxin Lin, Chengkou Liu, Wei He, Zhao Yang, Kai Guo
Abstract
A green and practical method for the synthesis of C-3 halogenated benzothiophenes and benzofurans from 2-alkynylthioanisoles or 2-alkynylanisoles and potassium halide was developed under transition-metal- and oxidant-free conditions, employing an assembled electrochemistry continuous-flow system. The carbon and platinum plates were used as the anode and cathode, respectively; KI or KBr not only served as a halogen source but also as an electrolyte. Moderate to good yields of C-3 halogenated benzothiophenes and benzofuran derivatives were obtained under constant current. Notably, the halogen could also be restored at the cathode to obtain C-3 dehalogenated benzothiophenes and benzofurans in high selectivity by adjusting the current and flow rate of the continuous-flow system. Moreover, this reaction could be easily scaled up with good efficiency in the continuous-flow system, which presents major advantages over reactions in a traditional batch.