Calix[4]arene-Bonded Nano Silica Gel as an New, Efficient and Reusable Catalyst for the Synthesis of Xanthenes

A novel calix[4]arene-bonded nano silica gel (C4A–SiO₂) is prepared by covalent attachment of a calix[4]arene derivative to nano silica gel. The structure and properties of C4A–SiO₂ were studied by Fourier Transform Infra-Red (FTIR), thermogravimetric (TG), elemental analysis (CHN), scanning electron microscopy (SEM), and surface area analysis (BET). In addition, the organocatalytic activity of C4A–SiO₂ for synthesis of some biologically active cores xanthenes was investigated by comparison of the yields and reaction times. The results prove that utilization of catalyst causes the reaction time reduction and yield expansion. Xanthene structures have been proved by FT-IR, ¹H NMR, ¹³C NMR and comparison of melting points. Easy work-up, acceptable reaction times, eco-friendly solvent, recyclable of catalyst and high yields are remarkable advantages of these processes. The catalyst C4A–SiO₂ is recyclable for at least five cycles without substantial loss of activity. Thus, C4A–SiO₂ can be introduced as an efficient organocatalyst in synthesis of xanthenes.