Nickel-Catalyzed Reductive Cyclization of Alkynes and Esters via Oxanickelacycle Formation and β-Oxygen Elimination

We report a nickel-catalyzed reductive cyclization of esters with alkynes under mild conditions. A series of phenyl esters underwent efficient conversion to the corresponding cyclic ketones in the presence of triethylsilane as a reductant. Detailed mechanistic investigations combining density functional theory (DFT) calculations and experimental studies revealed that the reaction proceeds through oxidative cycloaddition of the alkyne and carbonyl group of the ester to nickel, followed by a β-oxygen elimination step. This pathway is kinetically favored over direct oxidative addition of the ester C–O bond.