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

A visible-light-induced, external photocatalyst-free, site-selective C−H arylation of 4H-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(3H)-one, 3-phenylquinoxalin-2(1H)-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.