Gold- and Silver-Catalyzed Intramolecular Cyclizations of Indolylcyclopropenes for the Divergent Synthesis of Azepinoindoles and Spiroindoline Piperidines

Gold- and silver-catalyzed novel intramolecular cycloisomerizations of nitrogen or carbon-tethered indolylcyclopropenes to furnish biologically and pharmaceutically valuable azepino-[4,5-b]indole and spiro[indoline-3,4-piperidine] derivatives have been developed. Both reactions exhibit high chemoselectivity and stereospecificity through completely different reaction pathways. Based on mechanistic studies, it is well demonstrated that gold and silver catalysts act differently to promote the anti- and syn-addition and the steric effect of the catalysts play an important role to switch the addition mode, affording the catalyst-controlled-divergent synthesis.