Microwave-assisted Synthesis of Xanthones Promoted by Sulfonic Acid-Functionalized Graphene Oxide Catalysts

Xanthones and thioxanthones derivatives are interesting compounds, because of their well-known properties in the fields of medicinal and biological activities (anticancer, antioxidant, antimicrobial, antiviral, antiinflammatory, antiallergy, antihypertensive, antithrombotic and anti-Alzheimer activity, depending on their diverse structures). Therefore, their syntheses have attracted a large number of organic chemists[1]. Xanthones are usually synthesized using benzophenones or diaryl ethers as starting materials under harsh reaction conditions and often in the presence of strong acids or toxic metals as catalysts, but generally providing the desired products in low yields. Improvements have been achieved applying microwave irradiation especially in theterms of higher yields and shorter reaction times [2]. In this study, a new method for the chemical synthesis of xanthones is described. The title compounds have been synthesized in good yields under microwave irradiation from substituted 2-hydroxybenzoic acids and resorcinol in the presence of GO/SO3H as the catalyst.In preliminary experiments, the model reaction was carried out in refluxing solvents and solvent free conditions using solid acids.After 24 h, the yields of products were low ( 20%) with large amounts of starting materials remaining increasing reaction time and temperature did not affect the yield of the product. To improve the yield and optimize the reaction conditions, the same reaction was carried out under microwave irradiation. In this condition products were obtained in good to excellent yields (80-95%).The pure product was identified by ¹H NMR, ¹³C NMR and FT-IR spectroscopy (Figure 1).