Rh(III)-catalyzed oxidative annulation of 2-phenylimidazo[1,2-a]pyridines with alkynes: mono versus double C-H activation.

Rh(III)-catalyzed C-H activation of 2-phenylimidazo[1,2-a]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-a]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.