Visible‐Light Induced Ag‐Palladacycle‐Complex‐Mediated Regioselective C−H Arylation

Abstract A visible‐light‐induced, external photocatalyst‐free, site‐selective C−H arylation of 4 H ‐pyrido[1,2‐ a ]pyrimidin‐4‐ones and various 2‐aryl heteroarenes has been developed to provide ortho arylated products 41–95% yield at room temperature. A mechanistic study using control experiments, UV‐visible study, DFT study, and observation of colored aggregates suggest that in situ generated Ag‐palladacycle complex of 2‐aryl heteroarenes is responsible for absorbing the visible light and generating aryl radicals from aryldiazonium salts. Further, this methodology demonstrates its versatility by transforming various 2‐aryl heteroarenes, including 2‐phenylquinazolin‐4(3 H )‐one, 3‐phenylquinoxalin‐2(1 H )‐one, 2‐phenylpyridines, pyrazolo[1,5‐ a ]pyrimidines, 2‐phenylquinolines, 2‐phenylisoquinolines, and 2‐phenylbenzo[ d ]thiazoles, into their respective regio‐selective C−H arylated products under mild reaction conditions.