Intramolecular Csp2–Csp2 Friedel–Crafts Arylation: Substrate- and Condition-Controlled Divergent Synthesis of Fused-β-carbolines

A triple cooperative catalysis-mediated multicomponent reaction between 1-formyl-N-substituted-β-carbolines, a terminal alkyne, and a secondary amine allows access to unprecedented polycyclic β-carbolines via sequential A3-coupling and an intramolecular Csp2–Csp2 Friedel–Crafts arylation reaction. The reaction is successful in a dry inert atmosphere only with substrates bearing a methoxy-substituted benzyl group at the indole nitrogen. Conversely, treating 3-amino­indolizino­[8,7-b]­indoles (obtained after A3-coupling) with acid in the presence of H2O in air offers a general route to natural-alkaloid-like products.