Air-stable zirconium (IV)-salophen perfluorooctanesulfonate as a highly efficient and reusable catalyst for the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones/thiones under solvent-free conditions
An air-stable complex of zirconium (IV)-salophen perfluorooctanesulfonate ( 1 ) was successfully synthesized by reacting Zr (salphen)Cl 2 and C 8 F 17 SO 3 Ag. Complex 1 was characterized and studied by different techniques (NMR, IR, HRMS, TG-DSC, conductivity and acidity measurements), and was found to be air-stable, water tolerant, thermally stable and strongly Lewis-acidic. Complex 1 exhibited high catalytic efficiency for the synthesis of 3,4-dihydropyrimidin-2-(1H)-ones/thiones via the Biginelli reaction of aldehydes, 1,3-dicarbonyl compounds and urea/thiourea under solvent-free conditions. Furthermore, complex 1 could be reused 5 times with minimal changes in catalytic efficiency. Compared with previously reported methods, the important features of this protocol are the solvent-free conditions, the short reaction times, the wide substrate compatibility, the high efficiency and the good reusability.
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