Formal base-free homolytic aromatic substitutions via photoredox catalysis

We developed a simple and convenient method to assemble biaryls exploiting a photoredox catalyst and visible light. Diazonium salts generate aryl radicals that could then add on unactivated (hetero) arenes and the sequence eventually delivers products via formal homolytic aromatic substitutions. The direct C-H arylation of these usually unreactive substrates is achieved at room temperature using low catalyst loadings and shows broad functional group tolerance.