Methylene dipyridine nanoparticles stabilized on Fe3O4 as catalysts for efficient, green, and one-pot synthesis of pyrazolophthalazinyl spirooxindoles

• A methylene dipyridine based catalyst supported on Fe3O4 nanoparticles was synthesized.
• It was used as a recyclable catalyst for the synthesis of pyrazolophthalazinyl spirooxindoles.
• Pyrazolophthalazinyl spirooxindoles were obtained in good to high yields.
• In this method, catalyst separation was easily performable by a magnetic bar.

Surface functionalization of magnetic particles is an elegant way to bridge the gap between heterogeneous and homogeneous catalysis. The introduction of magnetic particles (MPs) in a variety of solid matrices allows the combination of well-known procedures for catalyst heterogenization with techniques for magnetic separation. We have conveniently loaded base groups on magnetic particles supports in which dipyridin-2-ylmethanol is used as aminating agent. The main targets are room temperature, solvent-free conditions, rapid (immediately) and easy immobilization technique, and low cost precursors for the preparation of highly active and stable MPs with high densities of functional groups. The inorganic, magnetic, solid base catalyst was characterized via Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The catalyst is active for the synthesis of pyrazolophthalazinyl spirooxindoles and the products are isolated in high to excellent yields (90–93%). Supporting this base catalyst on magnetic particles offers a simple and non-energy-intensive method for recovery and reuse of the catalyst by applying an external magnet. Isolated catalysts were reused for new rounds of reactions without significant loss of their catalytic activity.

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