Facile and Rapid Synthesis of 3,4-Dihydropyrimidin-2-(1H)-ones and Thione Derivatives Through the Biginelli Protocol Using N-Methylimidazolium Acetate

Some protic ionic liquids (PILs) were synthesized by the direct neutralization reaction of N-methylimidazole and 4-N,N-dimethylaminopyridine as nitrogen-containing heterocyclic organic bases with acetic acid and trifluoroacetic acid. The relative acidity of the prepared ionic liquids was evaluated by Hammet acidity function using UV-Vis spectroscopy. The catalytic effects of the obtained ionic liquids were investigated in the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones and thione derivatives through Biginelli reaction. Among N-methylimidazolium acetate [MImH][OAc], N-methylimidazolium trifluoroacetate [MImH][CF3CO2], 4-N,N-dimethylaminopyridinium acetate [DMAPH][OAc] and 4-N,N-dimethylaminopyridinium trifluoroacetate [DMAPH][CF3CO2], [MImH][OAc] provided the best results. Using 5 mol% of [MImH][OAc] as a catalyst, 3,4-dihydropyrimidin-2-(1H)-ones and thione derivatives were obtained in high to excellent yields at 100 ºC during 15-50 min.