A green one-pot three-component synthesis of tetrahydrobenzo[b]pyran and 3,4-dihydropyrano[c]chromene derivatives using a Fe3O4@SiO2–imid–PMAn magnetic nanocatalyst under ultrasonic irradiation or reflux conditions

Abstract

An efficient and environmentally benign procedure for the synthesis of tetrahydrobenzo[b]pyran and 3,4-dihydropyrano[c]chromene derivatives has been developed by a one-pot three-component reaction of various aldehydes, malononitrile, and dimedone or hydroxycoumarin in the presence of Fe₃O₄@SiO₂–imid–PMAⁿ nanoparticles as magnetic catalysts under ultrasonic irradiation or reflux conditions in water. This new procedure has notable advantages such as operational simplicity, excellent yields, short reaction time, and absence of any tedious workup or purification. In addition, the excellent catalytic performance in a water medium and the easy preparation, thermal stability and separation of the catalyst make it a good heterogeneous system and a useful alternative to other heterogeneous catalysts. Also, the catalyst can be easily recovered by a magnetic field and reused for eight consecutive reaction cycles without significant loss of activity.