Gold-catalyzed hydrative carbocyclization of 1,5- and 1,7-allenynes mediated by pi-allene complex: mechanistic evidence supported by the chirality transfer of allenyne substrates.

We report PPh3AuCl/AgOTf-catalyzed hydrative carbocyclization of 1,5- and 1,7-allenynes to give cyclized ketones chemoselectively. In this transformation, hydration occurrs regioselectively at the C[triple bond]CPh carbon, accompanied by addition of the C[triple bond]CPh carbon to the two terminal allenyl carbons. This method is effective for the construction of a quaternary carbon center. On the basis of the chirality transfer of allenyne substrates, control experiments, and theoretic calculations, we propose that this hydrative carbocyclization proceeds through an initial pi-allene complex with a small energy barrier.