Palladium/Norbornene-Catalyzed C-H/C-H [3 + 2] Annulation of Imidazopyridines with 2-Halobenzoic Acids via Six-Membered Palladacycles.

Herein we report an unprecedented palladium/norbornene-catalyzed C-H/C-H [3 + 2] annulation of imidazopyridines with 2-bromobenzoic acids, efficiently constructing ring-fused imidazo[1,2-]pyridine architectures with excellent functional tolerance. The resulting polycyclic (hetero)aromatic products demonstrate promising potential as fluorescent molecular scaffolds. Mechanistic studies identify the formation of a six-membered C-ANP intermediate in this domino conversion, which represents a distinct departure from classical five-membered palladacycles in Catellani-type reactions.