In this article, Fe3O4 nanoparticles, 2D Fe3O4/Mg(OH)2, and 2D Fe3O4/MgO nanocomposites were synthesized using ionic liquid [OMIM]Br as green designer and stabilizer at ambient pressure. Here, we report a special method for a sandwich like magnetic nanocomposites synthesis. The characterization of these nanocomposites was performed by IR, XRD, SEM, TEM, BET, and VSM techniques. Synthesized nanostructures were employed in the synthesis of 4H-chromene, 4H-pyran, and oxepine derivatives in three-component tandem reactions. Although, Fe3O4/Mg(OH)2 nanocomposite, as magnetically separable heterogeneous catalyst, has showed lower surface area in comparison to Fe3O4/MgO, exhibited a significant enhancement in the yield of the desired products. The described protocol has various advantages including simple work-up, mild reaction condition, green solvent, and the high atomic economy that make attractive procedure. The nanocatalysts exhibited remarkable reusable activity. Also, investigation of green chemistry metrics approved that Fe3O4/Mg(OH)2 nanocomposites play an essential role in the improvement of the reaction yield of 4H-chromene, among other products.