Synthesis of 8H‑Indolo[3,2,1-de]phenanthridin-8-ones via Pd(OAc)2‑Catalyzed Double Oxidative Coupling Dehydrogenations

A Pd(OAc)2-catalyzed self-coupling reaction of 2-bromo-N-arylbenzamides has been developed under basic conditions and in the presence of benzoic acid, unexpectedly producing 8H-indolo[3,2,1-de]phenanthridin-8-ones. The protocol involves Ullmann coupling and two consecutive oxidative coupling dehydrogenation steps, providing an efficient route for the production of fused pentacyclic indolophenanthridinone scaffolds with moderate to good yields.