3,4-Dihydropyrano [C] chromene Synthesis Using Fe3O4@SiO2-SO3H Magnetic Nanocatalyst

Synthesis of 4H-chromene and its derivatives has attracted great interest due to their biological and pharmacological activities. Here, a simple and practical method was employed for synthesizing 3,4-Dihydropyrano[c]chromene derivatives, which have found medicinal applications. This method involves reacting 4-hydroxycoumarin and malonitrile with an aromatic aldehyde in the presence of Fe3O4@SiO2-SO3H nanocatalyst and methanol as a green solvent. The prepared catalyst was characterized by FT-IR, XRD, BET, VSM, and SEM. The reaction was optimized for four variables of benzaldehyde derivatives, solvent type, temperature, and catalyst loading. The highest 3,4-Dihydropyrano [c]chromene yield of 98% was obtained with 1 mmol of 3-nitrobenzaldehyde and 0.05 g of Fe3O4@SiO2-SO3H at 80 °C in methanol solvent after 2h. Notably, the saturation magnetization of Fe3O4@SiO2-SO3H nanocomposites is sufficient for magnetic separation using an external magnet. This method yields excellent results with easy separation of catalyst. The recyclability test for five consecutive runs showed negligible loss in catalytic activity.