Synthesis of Indeno[1′,2′:4,5]imidazo[1,2‑a]pyridin-11-ones and Chromeno[4′,3′:4,5]imidazo[1,2‑a]pyridin-6-ones through Palladium-Catalyzed Cascade Reactions of 2‑(2-Bromophenyl)imidazo[1,2‑a]pyridines

A novel and efficient synthesis of 11H-indeno­[1′,2′:4,5]­imidazo­[1,2-a]­pyridin-11-one, a hybrid structure of indenone with imidazo­[1,2-a]­pyridine, from the reaction of 2-(2-bromophenyl)­imidazo­[1,2-a]­pyridine with carbon monoxide through palladium-catalyzed CO insertion and C–H bond activation, has been developed. Intriguingly, under similar conditions but in the presence of Cu­(OAc)2, the reaction selectively afforded 6H-chromeno­[4′,3′:4,5]­imidazo­[1,2-a]­pyridin-6-one, a hybrid structure of chromenone with imidazo­[1,2-a]­pyridine, via a more sophisticated cascade process including acetoxylation, deacetylation, CO insertion, and C–H bond activation.