γ-Fe₂O₃@Zn-LDH-EAE-SO₃H for multi-component synthesis of chromeno[4,3-<i>b</i>]quinoline-6,8-dione derivatives

In this study, 2-aminoethanesulfonic acid immobilized on epichlorohydrin-functionalized γ-Fe₂O₃@Zn-LDH (γ-Fe₂O₃@Zn-LDH-EAE-SO₃H) was synthesized as a new and efficient magnetic nanostructured catalyst for the rapid synthesis of chromeno[4,3-<i>b</i>]quinoline-6,8-dione derivatives. The nanostructured catalyst was subsequently characterized using various techniques including FT-IR, XRD, TEM, FE-SEM, EDX, EDX-mapping, TGA, CHNS and VSM analyses. The characterization results confirmed the composition of γ-Fe₂O₃@Zn-LDH-EAE-SO₃H and demonstrated that the magnetic nanoparticles were spherical in shape with average particle sizes ranging from 5 to 17 nm. As an excellent alternative to Brønsted acids, γ-Fe₂O₃@Zn-LDH-EAE-SO₃H exhibited high efficiency in the multi-component synthesis of chromeno[4,3-<i>b</i>]quinoline-6,8-dione derivatives in green media. In comparison to the conventional methods, this protocol presented several key benefits such as reduced reaction times, mild reaction conditions, simple work-up processes, pure products with high yields, easy catalyst recovery with an external magnetic field and the capability to reuse the catalyst several times without any significant loss in its catalytic activity. In addition, a notable feature of the present protocol was the use of ethanol as an environmentally friendly solvent, eliminating the use of toxic solvents.