DFT Mechanistic Investigation of the Gold(I)-Catalyzed Synthesis of Azepino[1,2-a]indoles

We describe a computational DFT investigation on the mecha- nism of the one-pot synthesis of azepino-indoles catalyzed by [Au(IPr)Cl]/AgOTf (IPr = 1,3-bis(2,6-diisopropylphenyl-imidazol- 2-ylidene) by the simultaneous construction of the pyrrolyl and seven-membered rings. The mechanism of the final ring-clos- ing event is elucidated, which reveals the counterion-assisted nucleophilic trapping of the carbonyl moiety by the alkenyl- gold species formed in situ. The computational evidence sup- ports the labeling control experiments and highlights the pres- ence of a cyclopropyl-gold-carbenoid intermediate in the final intramolecular 1,3-hydrogen-shift/skeleton-rearrangement se- quence.