Palladacycle-Catalyzed Methylenecyclopropanation of Bicyclic Alkenes with Propiolates

An efficient way to access functionalized methylenecyclopropanes has been developed by palladacycle-catalyzed cyclopropanation of bicyclic alkenes with propiolates in high yields. The structure of the palladacycle was kept intact in the reaction, shown by 31P NMR spectrum studies. A rational mechanism has been proposed with a deuterium-labeled experiment. The usefulness of the functionalized methylenecyclopropanes has also been demonstrated.