Palladium-catalyzed oxidative carbonylation of 1-alkynes into 2-alkynoates with molecular oxygen as oxidant

A new preparative method to produce alkyl 2-alkynoates from 1-alkynes in alcohol under atmospheric pressure of CO at room temperature was developed with palladium-phosphine catalysts, using molecular oxygen as an oxidant. On the basis of the behavior of model complexes such as methoxycarbonylpalladium and alkynylpalladium complexes, we propose a mechanism accounting for the catalytic carbonylation of alkynes through an intermediate having the both methoxycarbonyl and alkynyl ligands that liberates methyl 2-alkynoates and a Pd(0) species on reductive elimination. The oxidation of Pd(0) to Pd(II) species in the presence of a halide ion was confirmed to proceed cleanly with molecular oxygen as the oxidant. On the basis of the findings on homogeneous catalysts, a heterogeneous catalytic system using Pd/C has also been developed.