Gold-Catalyzed Cycloisomerization of o-Alkynylbenzaldehydes with a Pendant Unsaturated Bond: [3 + 2] Cycloaddition of Gold-Bound 1,3-Dipolar Species with Dipolarophiles

[reaction: see text] A new and novel Au-catalyzed cycloisomerization of ynals bearing a pendant unsaturated bond leading to synthetically valuable [6.7.n]-tricyclic compounds were developed. This study strongly supports the intermediacy of [3 + 2] cycloaddition proposed by DFT calculation and provides an easy access to key skeletons found in a variety of natural products.