Rh(III)-Catalyzed Oxidative Annulation of 2‑Phenylimidazo[1,2‑<i>a</i>]pyridines with Alkynes: Mono versus Double C–H Activation

Rh­(III)-catalyzed C–H activation of 2-phenylimidazo­[1,2-<i>a</i>]­pyridines in divergent oxidative coupling with alkynes has been achieved. Selective mono versus 2-fold C–H activation has been attained under condition control. When AgOAc was used as an oxidant, the coupling afforded 5,6-disubstituted naphtho­[1′,2′:4,5]­imidazo­[1,2-<i>a</i>]­pyridines as a result of initial nitrogen chelation-assisted C–H activation at the benzene ring followed by rollover C–H activation. In contrast, the reaction afforded a fused isoquinolinium salt as a result of C–C and C–N coupling when AgBF₄ was employed as a co-oxidant. A rhodacyclic intermediate has been isolated