Microwave-Assisted Synthesis of Heterocycles via Rhodium(III)-Catalyzed C–H Activation: Norbornadiene as an Acetylene Equivalent

General procedures for the rhodium-catalyzed annulation of aryl/heteroaryl O-pivaloyl hydroxamic acids and norbornadiene have been developed. Employing norbornadiene as an acetylene equivalent enables utilization of diverse heterocyclic substrates for this transformation which fail to react or undergo competitive Lossen rearrangement under previously reported conditions. Microwave heating significantly reduces reaction times compared to conventional protocols and allows a one-step process to be realized. The conditions described herein have been adapted for gram-scale synthesis and applied to the formal synthesis of Pfizer clinical candidates.