Domino Approach to Benzofurans by the Sequential Sonogashira/Hydroalkoxylation Couplings Catalyzed by New N-Heterocyclic-Carbene-Palladium Complexes

A set of three different NHC-Pd-pyridine complexes (NHC = 1,2,4-trimethyltriazolyldiylidene, 1,3-dimethylimidazolylidene, and 1,4-dimethyltriazolylidene have been prepared and fully characterized. The X-ray molecular structures of two of the complexes are reported. The three complexes have been tested in a series of reactions between o-hydroxyaryl halides and phenylacetylene to afford benzofurans, in a tandem process that comprises a Sonogashira coupling followed by a cyclic hydroalkoxylation. All three catalysts afforded excellent yields of the final products when the corresponding iodoarenes were used.