Electroreduction strategy: a sustainable tool for the generation of aryl radicals

Aryl radicals are important and versatile active intermediates in synthetic chemistry, and the chemical conversions involved are regarded as perfect complements to the transition-metal-catalyzed arylation reactions. The formation of aryl radicals is mainly achieved through reductive systems. Electrocatalysis has a safe and controllable potential range that can easily attain a reduction potential beyond the range of chemical reductants and excited photocatalysts, offering a synthetically attractive and environmentally friendly alternative for the production of aryl radicals. Remarkable achievements in the electrochemical functionalization of aryl radicals have been reported. This review primarily focuses on the generation of aryl radicals via an electroreduction strategy, and systematically elaborates on synthetic applications, scope, and limitations of the substrates. The full spectrum of aryl radical precursors applied in the electroreduction strategy, including aryl halides, aryl diazonium salts, arylazo sulfones, aryl amines, nitroarenes, aryl quaternary ammonium salts, aryl triflates, and aryl thianthrenium salts, is reviewed.