Protonolysis of the carbon-palladium bond in palladium(II)catalyzed enyne cyclization in imidazolium-type ionic liquids

摘要

The Pd-catalyzed cyclizations of 1,6-enynes are efficient reactions for the synthesis of alpha-methylene-gamma-butyrolactones and lactams. The effects of solvent, proton source, chloride concentration, and temperature on the protonolysis of the carbon-Pd bond were investigated and the optimal reaction conditions were identified. We showed that imidazolium-type ionic liquids played an important role in the reaction both as a ligand for the palladium catalyst and as a solvent. The crystal structure of the Pd complex was obtained and the reaction mechanisms were discussed. (C) 2008 Elsevier Ltd. All rights reserved.