Fe3O4@silica sulfuric acid nanoparticles: An efficient reusable nanomagnetic catalyst as potent solid acid for one-pot solvent-free synthesis of indazolo[2,1-b]phthalazine-triones and pyrazolo[1,2-b]phthalazine-diones

• Reusable nanomagnetic catalyst.
• One-pot solvent-free synthesis of indazolo[2,1-b]phthalazine-triones.
• One-pot solvent-free synthesis of pyrazolo[1,2-b]phthalazine-diones.
• Fe3O4@silica sulfuric acid core–shell composite.

Regarding the green chemistry's goals, silica-coated magnetite nanoparticles (MNPs) open up new avenue to introduce an amazing and efficient system for facilitating catalyst recovery in different organic reactions. Therefore, in this paper the preparation of sulfuric acid functionalized silica-coated magnetite nanoparticles with core–shell structure (Fe3O4@silica sulfuric acid) are presented by using Fe3O4 spheres as the core and silica sulfuric acid nanoparticles as the shell. The catalyst was characterized by infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) spectroscopy, and vibrating sample magnetometer (VSM). Ability of this nanomagnetic solid acid catalyst in the one-pot three-components condensation reaction of phthalhydrazide, aromatic aldehydes and cyclic or acyclic 1,3-diketones are also described. Utilization of easy reaction conditions, catalyst with high catalytic activity and good reusability, and simple magnetically work-up, makes this methodology as an interesting option for the economic synthesis of indazolo[2,1-b]phthalazine-triones and pyrazolo[1,2-b]phthalazine-diones.

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