Gold-catalyzed Bicyclization of Diaryl Alkynes: Synthesis of Polycyclic Fused Indole and Spirooxindole Derivatives

An unprecedented gold-catalyzed bicyclization reaction of diaryl alkynes has been developed for the synthesis of indoles in good to high yields. Mechanistically, this alkyne bifunctionalization transformation was terminated by a stepwise formal X–H insertion reaction to furnish the corresponding polycyclic-frameworks with structural diversity, and the key intermediate 3H-indole was isolated and characterized for the first time. In addition, further transformation of these generated tetracyclic-indoles with PCC as the oxidant provided straightforward access to the spirooxindoles in high yields.