PALLADIUM-CATALYZED ANNULATION OF INTERNAL ALKYNES BY ARENE-CONTAINING VINYLIC IODIDES AND TRIFLATES

In the presence of a palladium catalyst, internal alkynes undergo carb oannulation by cyclic and acyclic vinylic iodides and triflates bearin g a neighboring aromatic ring to produce a variety of carbocycles. For example, a number of 9,10-disubstituted-1,2,3,4-tetrahydrophenanthren es have been prepared in good yields through the palladium-catalyzed a nnulation of internal alkynes by 2-phenyl-1-cyclohexenyl triflate (1) or 1-iodo-2-phenylcyclohexene (2). This annulation process is fairly g eneral and highly regioselective. The process appears to involve oxida tive addition of the vinylic substrate to Pd(0) to produce a vinylic p alladium intermediate, which adds the carbon moiety to the less hinder ed end and the palladium to the more hindered end of the alkyne, follo wed by intramolecular ring closure onto the neighboring aryl group. Th e scope and limitations of this methodology are discussed.