2,2′-(Arylmethylene)bis(3-hydroxy-5,5-dimethylcyclohex-2-enone) crystals formation via atom economy reaction and their antioxidant activity

Functionalized graphene oxide by 4-amino-3-hydroxy-1-naphthalenesulfonic acid as a heterogeneous nanocatalyst for the one-pot synthesis of tetraketone and tetrahydrobenzo[b]pyran derivatives under green conditions

4-Amino-3-hydroxy-1-naphthalenesulfonic acid-functionalized graphene oxide (GO-ANSA) was prepared and characterized using different spectroscopic, microscopic and analytical methods including energy-dispersive X-ray spectroscopy (EDS), EDS elemental mapping, Fourier-transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and thermogravimetry/differential thermogravimetry analysis (TGA/DTA). The obtained nanomaterial was used as a novel, highly efficient, and reusable solid acid carbocatalyst for the one-pot three-component synthesis of tetraketone, as well as tetrahydrobenzo[b]pyran derivatives via tandem Knoevenagel-Michael reactions under green conditions. All of the derivatives were prepared in EtOH, as a green solvent, under reflux conditions in high to excellent yields and very short reaction times. The nanocatalyst was recovered and reused at least five times without significant reduction in its activity. In addition, the absence of toxic transition metals, high to excellent yields, mild reaction conditions, simple procedure for the separation and purification of products, stability, and recycling of the catalyst are the most important advantages of this green procedure.