Oxidative Cross-Coupling of Substituted Phenols with Unactivated Aromatics

Abstract

The cross‐coupling of substituted phenols or naphthols with substituted aromatics in the presence of K2S2O8 and Bu4N+·HSO4– in CF3COOH at ambient temperature is described. The cross‐coupling reaction provides unsymmetrical biaryls in good to moderate yields in a highly regioselective manner. A possible reaction mechanism was proposed and supported by UV/Vis and EPR studies. A regioselective C–H arylation of substituted phenols or naphthols with substituted aromatics in the presence of K2S2O8 and Bu4N+·HSO4– in CF3COOH at ambient temperature providing unsymmetrical biaryls is described. The cross‐coupling reaction is compatible with various substituted phenols and aromatics. Based on oxidation potential studies, it was observed that phenols with oxidation potentials up to 0.68 V and naphthols up to 0.88 V were compatible with the reaction. The cross‐coupling reaction proceeds through the reaction of K2S2O8 with substituted phenol, providing a cationic phenol radical intermediate that was further converted into the phenoxy radical intermediate by the dissociation of H+. Subsequent radical‐anion coupling of the phenoxy radical intermediate with a substituted aromatic affords the cross‐coupling product. The formation of a cationic phenol radical intermediate and phenoxy radical intermediate were confirmed by UV/Vis and EPR studies.