Mg-Al hydrotalcite as an efficient catalyst for microwave assisted regioselective 1,3-dipolar cycloaddition of nitrilimines with the enaminone derivatives: A green protocol

Abstract

Microwave assisted generation of in situ nitrilimines and their regioselective 1,3-dipolar cycloaddition reaction with enaminones to produce pyrazole derivatives by Mg-Al hydrotalcite (Mg-Al HT) catalyst is introduced. Short reaction times with high yields (90-94%), the absence of an organic solvent and reuse of the catalyst for at least five times without loss of activity could regard as cost effective, environmentally friendly and greener process. The fresh and used catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectroscopy, N2 physisorption and temperature programmed desorption by CO2 (CO 2-TPD) to understand the role of hydrotalcite in the reaction mechanism and the robust nature of the catalyst. It appears that better microwave absorptivity of the catalyst with Mg-Al HT structure might be responsible for shorter reaction times with high yields. A plausible mechanism for 1,3-dipolar cycloaddition over the Mg-Al HT is proposed. © 2012 Elsevier B.V. All rights reserved.