Palladium-catalyzed annulation of internal alkynes by arene-containing vinylic iodides and triflates

In the presence of a palladium catalyst, internal alkynes undergo carboannulation by cyclic and acyclic vinylic iodides and triflates bearing a neighboring aromatic ring to produce a variety of carbocycles. For example, a number of 9,10-disubstituted-1,2,3,4-tetrahydrophenanthrenes have been prepared in good yields through the palladium-catalyzed annulation of internal alkynes by 2-phenyl-1-cyclohexenyl triflate (1) or 1-iodo-2-phenylcyclohexene (2). This annulation process is fairly general and highly regioselective. The process appears to involve oxidative addition of the vinylic substrate to Pd(0) to produce a vinylic palladium intermediate, which adds the carbon moiety to the less hindered end and the palladium to the more hindered end of the alkyne, followed by intramolecular ring closure onto the neighboring aryl group. The scope and limitations of this methodology are discussed.