Synthesis of indolizines through aldehyde–amine–alkyne couplings using metal-organic framework Cu-MOF-74 as an efficient heterogeneous catalyst

Abstract

A crystalline 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 exhibited high catalytic activity in the synthesis of indolizines through aldehyde-amine-alkyne three-component coupling transformation and higher than those of other Cu-MOFs such as Cu₂(BDC)₂(DABCO), Cu₃(BTC)₂, Cu(BDC), Cu₂(NDC)₂(DABCO), and Cu₄I₄(DABCO)₂. The reactions could only proceed to produce indolizines in the presence of the solid Cu-MOF catalyst, and contribution from active copper species leached from the solid Cu-MOF-74, if any, was negligible. The Cu-MOF catalyst be recovered and reused several times for the synthesis of indolizines without a significant degradation in catalytic activity. To the best of our knowledge, the synthesis of indolizines using a recyclable heterogeneous catalyst was not previously mentioned in the literature.