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Indium-based metal-organic frameworks as catalysts: synthesis of 2-nitro-3-arylimidazo[1,2-a] pyridines via oxidative amination under air using MIL-68(In) as an effective heterogeneous catalyst † The metal-organic framework MIL-68(In) has emerged as a productive heterogeneous catalyst for the synthesis of 2-nitro-3-arylimidazo[1,2-a]pyridines via oxidative amination between 2-aminopyridines and nitroalkenes using air as an oxidation agent. The catalyst displayed impressively higher efficiency for the generation of 2-nitro-3-arylimidazo[1,2-a]pyridines than various other MOFs and several common homogeneous catalysts. Heterogeneous catalysis was verified for the reaction of 2-aminopyridines with nitroalkenes employing the framework-based catalyst. It was possible to collect and reuse the catalyst for the production of 2-nitro-3-arylimidazo[1,2-a]pyridines without a pronounced deterioration in catalytic efficiency. To the best of our knowledge, the preparation of 2-nitro-3-arylimidazo[1,2-a] pyridines has not been formerly conducted utilizing heterogeneous catalysts. Furthermore, indium-based catalysts were not previously employed for this transformation. Scheme 1 Synthesis of 2-nitro-3-phenylimidazo[1,2-a]pyridine utilizing MIL-68(In) catalyst. Fig. 1 Yields of 2-nitro-3-phenylimidazo[1,2-a]pyridine at varied temperatures.

A new pathway to access pyrido-fused quinazolinones via a Cu(OAc)2-catalyzed domino sequential transformation between 2′-haloacetophenones and 2-aminopyridines was demonstrated.