Synthesis of imidazo[1,5-a]pyridines via oxidative amination of the C(sp3)–H bond under air using metal–organic framework Cu-MOF-74 as an efficient heterogeneous catalyst

Abstract

A crystalline porous copper-based metal–organic framework Cu-MOF-74 was synthesized, and was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), atomic absorption spectrophotometry (AAS), and nitrogen physisorption measurements. The Cu-MOF-74 used was a recyclable catalyst for the condensation–cyclization reaction between 2-benzoyl pyridine and different benzylamines via oxidative amination of the C(sp³)–H bond to form 1,3-diarylated imidazo[1,5-a]pyridines using air as the oxidant. The Cu-MOF-74 exhibited better catalytic activity for the transformation than other MOFs including Cu(BDC), Cu₂(BDC)₂(DABCO), Cu₃(BTC)₂, Cu₂(BPDC)₂(BPY), Cu(OBA), Cu₂(OBA)₂(BPY), and Cu(INA)₂. The solid catalyst could be recovered and reused several times without a significant degradation in catalytic activity. To the best of our knowledge, the synthesis of 1,3-diarylated imidazo[1,5-a]pyridines via oxidative amination of the C(sp³)–H bond was not previously performed under heterogeneous catalysis conditions.