Replacing sulfuric acid with water in electrochemical metal-free mild aromatic C–H amidation: a direct route to N-phenylamides

Abstract

In this work, we describe a mild electro-oxidative metal-, oxidant- and acid-free direct amidation of aromatic C–H bonds using nitrile solvents as a source of amide and amine moieties. We show that carrying out the reaction in a divided cell makes it possible to eliminate the use of an acid used in previous attempts, enabling at the same time this reaction for easily reducible substrates and paired electrosynthesis. This electrochemical approach was demonstrated on 60 examples of N-phenylamides, including propanil, which has not been obtained under electrochemical conditions so far, and 12 examples of benzoxazoles; it is also amenable to gram-scale synthesis. Mechanistic studies (voltammetry, EPR, and quantum chemical calculations) revealed that the process is initiated by the formation of hydroxyl radicals from residual water molecules on the anode, which attack the nitrile solvent, and the resulting amide radicals add to the arene.