Azocinoindole synthesis by a gold(I)-catalyzed ring expansion of 2-propargyl-β-tetrahydrocarboline.

A new methodology taking advantage of gold(I)-catalyzed ring expansion has been developed to assemble tricyclic 1H-azocino[5,4-b]indoles from 2-propargyl-β-tetrahydrocarbolines. The azocinoindoles were obtained in moderate to excellent yields; the structure of which was established by X-ray crystallographic analysis. A mechanism involving regioselective intramolecular hydroarylation, [1,2]-alkenyl migration and carbon-carbon bond-fragmentation was proposed.