Solvent-Free Microwave-Assisted Multicomponent Synthesis of 4H-Chromenes Using Fe3O4-Based Hydrotalcites as Bifunctional Catalysts

Magnetic Fe3O4-based hydrotalcites were used as bifunctional catalysts for the microwave-assisted solvent-free synthesis of 4H-chromene derivatives by a three-component reaction from (hetero)aromatic aldehydes, malononitrile, and naphthol derivatives. Structures of 4H-chromenes 4 d and 4 g were studied and confirmed by single-crystal X-ray diffraction analysis. The heterogeneous catalysts were synthesized by the co-precipitation method incorporating divalent metal cations such as Ni2+ or Co2+ in LDH-Mg. This multicomponent protocol allows the synthesis of diverse 4H-chromenes in 88-95 % yields, reduced reaction time, high atom economy, broad substrate scope, and operational simplicity. The reusability of the catalyst up to five recycles without appreciable loss of its catalytic activity, make the present protocol sustainable and advantageous compared to conventional methods.