CuCl(2)-induced regiospecifical synthesis of benzene derivatives in the palladium-catalyzed cyclotrimerization of alkynes.

Many metals or their complexes can catalyze the cyclotrimerization of alkynes to give benzene derivatives.1-9 Among these catalysts, palladium chloride10 and its bis(benzonitrile) complex11 are the most convenient. In these reactions, the yields of benzene derivatives generally depend on the substituents of alkynes. In the past 50 years, the regioand chemoselectivity for the cyclotrimerization of alkynes are the major challenge of synthetic chemists.12 In this paper, we wish to report a regioselective and highly chemoselective method for preparing benzene derivatives via palladium chloridecatalyzed cyclotrimerization of alkynes in the presence of CuCl2.