Catalytic Deamino-Diels–Alder and Formal [2+2+2] Annulation Enabled by Indolyl-Vinyl-Iminium as a C4 Synthon: Divergent Assembly of Indole Polycyclic Skeletons

Abstract Herein, we report indolyl-vinyl-iminium as a new C4 synthon. It enables the divergent assembly of indole polycyclic skeletons via cascade cyclizations, including a gold(I)-catalyzed intramolecular deamino-Diels–Alder reaction for the construction of benzo[b]carbazoles and a sequential gold(I)/HNTf2-catalyzed intermolecular formal [2+2+2] annulation that affords a broad spectrum of hexahydroindolo[2,3-b]carbazole derivatives. Theoretical calculations and control experiments shed light on the reaction mechanism and the origin of the diastereoselectivity.