Palladium catalyzed [2+2+1] cyclotrimerization of alkynes: selective synthesis of fulvenes

This is the first report on the selective synthesis of fulvenes via a [2+2+1] cyclotrimerization of alkynes under catalytic conditions. The reactions of aliphatic terminal alkynes 1a–e in the presence of a palladium catalyst in toluene gave the cyclotrimerization products 2a–e, not easily available through the previously known methods, in good to fair yields.