Cobalt(III)-Catalyzed [4+2] Annulation of Heterobicyclic Alkenes by sp2 C-H Activation

An efficient and convenient cobalt(III)-catalyzed highly diastereoselective strategy was demonstrated for the synthesis of epoxybenzophenanthridinone derivatives. The sp(2) C-H activation of N-methoxybenzamides and their annulation reaction with 7-oxa/aza benzonorbornadienes proceeds under mild conditions and exhibits excellent functional group tolerance. In addition, the products were transformed to biologically relevant phenanthridinones by an acid-catalyzed ring opening/aromatization sequence.