A Chemo- and Regioselective Tandem [3+2]Heteroannulation Strategy for Carbazole Synthesis: Synergizing Two Mechanistically Distinct Bond-Forming Processes

A modular approach to prepare tri- and tetracyclic carbazoles by a sequential [3+2]heteroannulation is described. First, op-timization of a Pd-catalyzed Buchwald-Hartwig amination followed by C/N-arylation in a one-pot process is established. Second, mechanistic analyses identified the origins of chemo- and regioselective sequential control of both bond-forming steps. Finally, the substrate scope is demonstrated by the preparation of a range of tri- and tetracyclic carbazoles, including expedient access to several natural products and anti-cancer agents.