Multicomponent synthesis of pyranopyrazoles using a MOF nanocatalyst (Cu(II)@UiO-66-AST) under green conditions

Abstract

A metal-organic framework (Cu(II)@UiO-66-AST) was used as an acidic nanocatalyst in the four-component reactions of hydrazine, aryl aldehydes, malononitrile, and acetylenic ester that led to pyranopyrazoles. The results clearly show that Cu@UiO-66-AST has a higher catalytic activity than UiO-66-NH₂ and Cu(OAc)₂. It could be due to the increase of dispersibility of Cu²⁺ by the formation of several stable complexes between Cu²⁺ ions and functional groups of ligand Azosulfathiazole (OH, CN, NH, and C-S) on the surface of the nanocatalyst. The advantages of this method include short reaction time (8 min), excellent yield (89–97 %), the use of a green solvent (EtOH), and the use of reusable nanocatalysts. It is noticeable, that the efficiency of Cu(II)@UiO-66-AST didn't show significant change after five consecutive cycles. Also, an evaluation of green metrics such as the E-factor (≤0.2), and atom economy (82.9–87.1 %), quantitatively prove the environmental friendliness of the method.