Addition of 1,3-dicarbonyl compounds to terminal alkynes catalyzed by a cationic cobalt(iii) complex

The Nakamura reaction using a cationic cobalt(iii) complex, [Cp*Co(CH₃CN)₃][SbF₆]₂ as the catalyst under neutral and aerobic conditions at 110 °C has been described. In solution, the complex is expected to lose a hemilabile acetonitrile ligand to produce a highly electron-deficient cobalt(iii) center, and the Lewis acidic nature of the cobalt center has been exploited for the enolization of the dicarbonyl compounds. The reaction of 1,3-dicarbonyl compounds with alkynes affords the corresponding alkenyl derivative. However, the reaction of phenylacetylene and its derivatives with β-ketoesters affords corresponding terphenyl compounds. Details of the mechanisms of the reactions have been proposed based on in situ LCMS measurements.