Green and Efficient Synthesis of Thiazolo [3,2-a]pyrimidin-3(5H)-one Derivatives under Catalyst-Free Conditions

Abstract

Heterocycles containing sulphur and nitrogen atoms in the core structure, possess a number of pharmacologically and biologically active compounds. So, in the past decade, various fused pyrimidines including purines, pteridines, quinazolines, pyridopyrimidines, triazolopyrimidines, pyrazolopyrimidines, pyrimidoazepines, furopyrimidines and pyrrolopyrimidines were studied and were found to possess remarkable pharmacological properties. Thus, our work was focused on the development of novel, green and efficient method for the synthesis of a series of 6-acetyl-7-methyl-5-aryl-2H-thiazolo[3,2- a]pyrimidin-3(5H)-one derivatives using 5-acetyl-6-methyl-4-aryl-3,4-dihydropyrimidin-2(1H)-thione derivatives as starting materials. The precursor pyrimidine derivatives were prepared by Biginelli reaction of pentan-2,4-dione, thiourea and an appropriate aromatic aldehyde in the presence of an ionic liquid, and then reacted with ethyl bromoacetate in a concise sequence involving condensation/cyclization reaction to give the corresponding thiazolopyrimidines in good yields under catalyst-free conditions in the presence of acetone as solvent. The structure of the whole synthesized compounds was determined by NMR and IR spectroscopy, and a plausible mechanism of their formation was proposed.