Ruthenium-catalyzed dimerization of propiolates: a simple route to α-pyrones.

A ruthenium-catalyzed regioselective intermolecular multistep homo- and heterodimerization of substituted propiolates providing α-pyrone-5-carboxylates and α-pyrone-6-carboxylates is described. The synthetic utilities of α-pyrone derivatives are shown. The proposed mechanism is strongly supported by experimental evidence.