Magnetic Fe ₃ O ₄ @BTC nanocomposite for ultrasound-assisted synthesis of dihydropyrano[2,3- <i>c</i> ]pyrazoles

We report an efficient approach for the synthesis of medicinally important dihydropyrano[2,3-<i>c</i>]pyrazoles derivatives by using Fe₃O₄@BTC nanocomposite (NCs) based catalytic system. The Fe₃O₄@BTC NCs were successfully synthesised <i>via</i>. immobilizing benzene-1,3,5-tricarboxylic acid (BTC) on Fe₃O₄ magnetic nanoparticles (MNPs). The synthesised NCs were characterized using X-ray diffraction (XRD) which disclose the formation of a crystalline structure of Fe₃O₄@BTC NCs, Fourier transform infrared (FTIR) spectroscopy suggests the presence of Fe-O band at 576 cm^-1 in addition to -C[double bond, length as m-dash]O, -O-H stretching frequencies are also observed, field emission scanning electron microscopy (FE-SEM) represents the spherical shape of Fe₃O₄@BTC NCs, high resolution-transmission electron microscopy (HR-TEM) revealed the particle size tobe ∼10.335 nm, energy dispersive analysis of X-ray (EDAX) shows the presence of Fe, C and O elements, Brunauer-Emmett-Teller (BET) surface area reveals its specific surface area 84.87 m² g^-1 and thermogravimetric analysis (TGA) shows its exceptional higher thermal stability. Furthermore, all dihydropyrano[2,3-<i>c</i>]pyrazoles derivatives were synthesised with high yield (79-92%), in shorter time (4-12 min). Recyclability of NCs was also investigated and it was found that the NCs can be reused over five cycles without any significant loss in its activity. Significantly, this protocol has prominent benefits such as high yields of product, shorter reaction time, facile workup, recyclable, use of ultrasound as clean energy source and absence of toxic solvents.