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

Abstract

A green and practical electrochemical method for the synthesis of C-3-sulfonated benzothiophenes from 2-alkynylthioanisoles and sodium sulfinates was developed under oxidant- and catalyst-free conditions. Moderate to good yields of sulfonated benzothiophenes bearing important and useful functional groups have been achieved at a constant current. Preliminary mechanistic studies indicated a tandem radical addition–cyclization pathway. Moreover, the protocol is easy to scale up and exhibits good reaction efficiency.

Electrochemical Synthesis of Polysubstituted Sulfonated Pyrazoles via Cascade Intermolecular Condensation, Radical–Radical Cross Coupling Sulfonylation, and Pyrazole Annulation

“…Cyclic voltammograms were recorded on a CHI 660E potentiostat. Compounds 3a – 3b , 3d , 3f – 3g , 3m – 3n , 3r – 3t , 3v , 3x – 3zc , 5a , 5c – 5n , 5p – 5r , 8 , 9 , 10 , 12 , 13 , 17 , 18 , 20 , and 21 are known, and their spectroscopic features are in good agreement with those reported in the literature.…”

Oxidation Potential-Guided Electrochemical Radical–Radical Cross-Coupling Approaches to 3-Sulfonylated Imidazopyridines and Indolizines

“…Even more, the necessity of photocatalyst and redox reagents can be eliminated in the electrochemical synthesis, where the direct anodic oxidation of sodium sulfinates to sulfonyl radicals can be performed (Scheme a). Thus, the sulfonyl radicals have been added to various radical acceptors such as alkenes, alkynes, and arenes under the electrochemical conditions . Since heteroarenes can be also anodically oxidized to radical cation species, the simple measurements of cyclic voltammetry of sodium sulfinates and heteroarenes can provide the total amount of voltage required for the electrochemical radical–radical cross-coupling processes .…”

Electro-organic synthesis: an environmentally benign alternative for heterocycle synthesis

“…Moreover, sevenmembered rings could also be formed in an efficient way through this transformation. Lastly, the scope of the protocol Recently Dong Zhang et al 113 designed a catalyst and oxidant-free electro-organic synthesis of C-3-sulfonated benzothiophenes (106). To optimise the reaction conditions, the initial pre-screening of the reaction was performed with 2-alkynylthio-anisoles (104a) and sodium p-toluenesulfinate (105a).…”