Highly Efficient and Selective Electrochemical Synthesis of Substituted Benzothiophenes and Benzofurans in Microcontinuous Flow

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 continuousflow system, which presents major advantages over reactions in a traditional batch.

Oxidant- and Catalyst-Free Synthesis of Sulfonated Benzothiophenes via Electrooxidative Tandem Cyclization

“…Subsequently, the sulfonyl radical III undergoes intermolecular radical addition to the alkynyl moiety of 1a to give the vinyl radical intermediate IV . Then, the intermediate IV is attacked by the methylthio moiety to afford the desired product 3a along with the release of the methyl radical. − The methyl radical is then converted into methane with the hydrogen from the reaction mixture.…”

Tunable Electrocatalytic Annulations of o-Arylalkynylanilines: Green and Switchable Syntheses of Skeletally Diverse Indoles

“…Based on the above results and the reported literature, ,, possible mechanisms for switchable formation of three types of indoles were proposed in Scheme . As illustrated in Scheme , the initial step is the anodic oxidation of iodide ion to generate iodonium (I + ) species with loss of two electrons.…”

Electrochemical Oxidative ortho‐Selective Trifluoromethylation of N‐Arylamides

“…Moreover, benzanilides bearing halogens (F, Cl, Br and I) at the para ‐position reacted to afford corresponding products (3h–3k) in 27–63 %. Only 27 % yields of the product 3k was obtained, maybe because of the instability of C−I bonds in electrochemical system [10] . In addition, the reactions of meta ‐ and ortho ‐substituted benzanilides at benzoyl groups, including those containing Me, CF 3 , F, Cl, Br, also generated the ortho ‐trifluoromethylation products (3l–3u) in 39–82 % yields.…”

“…Only 27 % yields of the product 3k was obtained, maybe because of the instability of CÀ I bonds in electrochemical system. [10] In addition, the reactions of meta-and ortho-substituted benzanilides at benzoyl groups, including those containing Me, CF 3 , F, Cl, Br, also generated the orthotrifluoromethylation products (3l-3u) in 39-82 % yields. Besides mono-substituted benzanilides, di-substituted benzanilides reacted with CF 3 SO 2 Na to give 3 v in 65 % yields.…”