Photo-Induced Sonogashira C-C Coupling Reaction Catalyzed by Simple Copper(I) Chloride Salt at Room Temperature

The conventional thermal Sonogashira C?C coupling reaction requires the use of a palladium catalyst and a large amount of ligands. Although there were a few reports describing the use of inexpensive metal catalysts, such as, copper (Cu), iron (Fe), and nickel (Ni), for replacement of palladium (Pd) in the Sonogashira reactions, it was later questioned that the observed effects were due to ppb levels contamination of Pd present in the reagents used in the reactions. Herein, we report that simple copper(I) chloride (CuCl) salt, in the absence of Pd and ligands, can catalyze the Sonogashira reaction with high yields (8099%) under blue LED light irradiation at room temperature. Control experiments show that no cross-coupling product was formed, when palladium(II) chloride (PdCl2) was used to replace CuCl as a catalyst. A series of electron-rich and electron-poor substituted aryl halides (bromides and iodides) as well as aryl- and alkylacetylenes are examined and the reaction mechanism is discussed.