In the present study, Fe 2+ and Ni 2+ immobilized on hydroxyapatite-core-shell γ-Fe 2 O 3 (γ-Fe 2 O 3 @HAp-Fe 2+ and γ-Fe 2 O 3 @HAp-Ni 2+ ) with a high surface area has been synthesized and characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), and scanning electron microscope (SEM) techniques. Then, γ-Fe 2 O 3 @HAp-Fe 2+ and γ-Fe 2 O 3 @HAp-Ni 2+ were used as a new and magnetically recoverable nano catalyst for the selective oxidation of sulfides to sulfoxides with 33% aqueous H 2 O 2 (0.5 mL) as an oxidant at room temperature in good to excellent yields and short reaction time. Nontoxicity of reagent, mild reaction condition, inexpensive and high catalytic activity, simple experimental procedure, short period of conversion and excellent yields, and ease of recovery from the reaction mixture using an external magnet are the advantages of the present method.

In this study, Ag, Ni2+, and Fe2+ immobilized on hydroxyapatite‐core‐shell γ‐Fe2O3 nanoparticles (γ‐Fe2O3@HAp‐Ag, γ‐Fe2O3@HAp‐Ni2+, and γ‐Fe2O3@HAp‐Fe2+) as a new and reusable Lewis acid magnetic nanocatalyst was successfully synthesized and reported for an atom economic, extremely facile, and environmentally benign procedure for the synthesis of highly functionalized tetrahydropyridines derivatives 4a‐t is described by one‐pot five‐component reaction of 2 equiv of aldehydes 1, 2 equiv of amines 2, and 1 equiv of methyl acetoacetate 3 in EtOH at room temperature in good to high yields and short reaction time. The presented methodology offers several advantages such as easy work‐up procedure, reusability of the magnetic nanocatalyst, operational simplicity, green synthesis avoiding toxic reagents and solvent, mild reaction conditions, and no tedious column chromatographic separation.

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Novel pyrimido[4,5-b]quinolines and pyrido[2,3-d:6,5-d ′ ]dipyrimidine derivatives were synthesized in one-pot, three-component approach using sulfonic acid supported on hydroxyapatite-encapsulated-γ-Fe 2 O 3 [γ-Fe 2 O 3 @HAp-SO 3 H] as magnetically recoverable nanocatalyst. The protocol provided a rapid, useful and green method for the preparation of the products in short reaction times and high yields.