Facile Synthesis of Pyrazolopyranopyrimidines by Synergism of Ultrasound Irradiation and Biocompatible Inulin Biopolymer as Catalyst

Abstract

Inulin, a natural polysaccharide has been utilized as a novel biodegradable, efficient, and environmentally benign catalyst for the ultrasound‐assisted one‐pot, single‐step multicomponent formation of a library of pyrazolopyrano[2,3‐d]pyrimidine‐diones 5(a‐k) from the reaction of ethyl acetoacetate, hydrazine hydrate, aromatic aldehydes, and barbituric/ thiobarbituric acid in aqueous ethanol (1 : 1) at 50 °C. This facile methodology offers a metal‐free, sustainable, selective synthesis of pyrazolopyrano[2,3‐d]pyrimidine‐diones with no by‐product having excellent product yield (≥90 %) in a shorter reaction time. Additionally, the biocompatible inulin is recyclable for up to five consecutive runs without much decrease in its catalytic potential. Inulin has been characterized by spectral techniques such as XRD, FTIR, Raman, and SEM. It shows remarkable stability in the reaction medium as evident from the zeta potential value of −21.39 mV and hydrodynamic diameter of 459.5 nm. Novel pyrazolopyrano[2,3‐d]pyrimidine‐diones (5g, 5h, 5j, and 5k) were also synthesized using this protocol and the synthesized compounds were examined for their antimicrobial activity.