Ni-Catalyzed [2+2+2] Cycloaddition of Alkynes to Form Arenes and Pyridines at Low Catalyst Loadings

We report the Ni-catalyzed cyclotrimerization of terminal alkynes at very low loadings of catalysts (0.05 mol% for all substrates). The nickel catalyst containing a terphenyl phosphine ligand allows carrying out the reactions at room temperature in only 30 min, providing the arene products as a single regioisomer in most cases The Ni complex is also competent for the synthesis of polysubstituted pyridines through the cycloadditions of diynes and nitriles at mild temperatures (25 º or 50 ºC) and low Ni loadings (1 mol%). Experimental data and computational studies support the involvement of monoligated PNi species in all fundamental steps of the catalytic cycle.