Thiourea dioxide‐grafted γ‐Fe2O3/HAp magnetic nanoparticles: Efficient, green and reusable nanocatalyst for synthesis of pyranopyridine derivatives

A novel thiourea dioxide‐functionalized hydroxyapatite‐encapsulated hybrid core‐shell γ‐Fe2O3@HAp‐TUD nanoparticles (MNPs) were prepared and characterized by FT‐IR, EDX, SEM, XRD, TGA and VSM analytical methods. The catalytic activity of these MNPs was evaluated through one‐pot three‐component reactions between various substituted aldehydes, malononitrile and 3‐cyano‐6‐hydroxy‐4‐methyl‐pyridin‐2(1H)‐one to afford the corresponding pyrano[2,3‐b]pyridines in high yields under mild and solvent‐free conditions. The catalyst can be easily recycled in a magnetic field and reused in five consecutive runs without significant decrease of its catalytic activity. An efficient and convenient procedure has been described for one‐pot multi‐component synthesis of pyrano[2,3‐b]pyridines derivatives in the presence of γ‐Fe2O3@HAP‐TUD MNPs as a heterogeneous catalyst. The reactions proceeded smoothly under solvent free condition to afford the corresponding products in quantitative yields. The catalyst can be easily recovered by an external magnet and reused for several successive fresh runs with no significant loss of catalytic activity.