Synthesis of Azocino[5,4-b]indoles via Gold-Catalyzed Intramolecular Alkyne Hydroarylation

An efficient procedure for the synthesis of the azocino[5,4-b]indole framework is presented, relying on a cationic gold-catalyzed intramolecular alkyne hydroarylation of propargylic amides derived from various tryptamines and 3-substituted 2-propynoic acids. The triphenylphosphinegold(I) chloride/silver(I) triflate catalytic system was found to be superior to our previously described mercury(II) triflate catalyst, and hence the substrate scope of the process was significantly expanded.