Rare‐Earth‐Metal‐Catalyzed Synthesis of Azaindolines and Naphthyridines via C−H Cyclization of Functionalized Pyridines

We report herein a rare‐earth‐metal‐catalyzed insertion of a 2‐pyridine C(sp2)−H bond into an intramolecular unactivated vinyl bond. This reaction provides streamlined access to a range of azaindolines in moderate to excellent yields. The salient features of this reaction include simple and mild reaction conditions, 100% atom efficiency, and wide substrate scope. This methodology is also used to construct other nitrogen‐containing compounds such as naphthyridine derivatives. A plausible mechanism for the formation of azaindolines involving initial C−H bond activation by the lanthanide complex followed by C=C insertion into a Ln−C bond to form an alkyl lanthanide species that subsequently undergoes cyclization is proposed.