Synthesis of Medium-sized 3,4-Annulated Imidazo[1,2-a]pyridines

An efficient approach to the hitherto unknown oxazabenzocyclooctaindenes, 3,4-annulated imidazo[1,2-a]pyridines containing an eight-membered ring, is described. The synthesis is based on a combination of regioselective Suzuki-Miyaura cross-coupling, copper-mediated C–O coupling, and, finally, intramolecular Pd-catalyzed C–H activation reactions. Optimization of the conditions of the latter step allowed for the challenging formation of the medium-sized ring in good to excellent yields.