Discovery of Oxygen Induced Chemoselectivity in Pd-Catalyzed C-H Functionalization: Cross-Dehydrogenative Coupling vs C-H Amination.

Abstract

We have come across a substrate namely, 5-benzoyl-pyrrolo[2,1-a]isoquinoline in which three different functionalizable C-H bonds were identified that could be judiciously transformed site selectively for the generation of complex polyring fused N-heterocycles. A Pd-catalyzed cross-dehydrogenative coupling of 5-benzoyl-pyrrolo[2,1-a]isoquinoline afforded 8H-indeno-pyrrolo[2,1-a]isoquinolinone and an oxygen induced palladium catalyzed selective C-H amination in the same substrate provided a pentacene viz., 9H-indolo-pyrrolo[2,1-a]isoquinoline. We also observed the formation of a multiring fused benzazepine scaffold by the site selective C-H amination in 5-(4-nitro benzoyl)-pyrrolo[2,1-a]isoquinoline.