Introduction of Click Synthesized Novel Organic-Inorganic Solid Acid Catalysts for Highly Promoted Synthesis of Substituted Xanthenes

Abstract

Herein, two new organic-inorganic Brønsted acidic ionic solids with phosphotungstate anion (BAIS-PW) based on click synthesis strategy are introduced for the efficient synthesis of highly substituted xanthenes. The approach to achieve these BAIS-PW organic-inorganic hybrids includes three-step consecutive reactions. At the first step, mono and di-substituted-1H-1,2,3-triazoles were prepared under click preparation conditions. In the second step, the prepared 1,2,3-triazole substrates were reacted with 1,4-butanesultone to give targeted 1,2,3-triazolium-N-butyl sulfonate zwitterions. In the final step, organic zwitterions were treated with aqueous solution of phosphotungstic acid to achieve the desired BAIS-PW organic-inorganic hybrids with organic 1,2,3-triazolum cation and phosphotungstate anion. This is the first report describing the preparation of BAIS using click chemistry. The prepared BAIS-PW hybrids were well characterized and confirmed using FTIR, 1H and 13C NMR, XRD, elemental analysis (CHNS), DSC and TGA techniques. The introduced BAIS catalysts have good thermal stability. The catalytic efficiency of the introduced SO3H-functionalized organic-inorganic catalysts was examined for the one-pot synthesis of substituted xanthenes. It was found that low amount of BAIS catalysts (10 mmol%) is optimized amount to achieve desired substituted xanthenes under solvent free conditions in short times (5–10 min) with high isolated yields (90–95%) and high turnover number (TON) and turnover frequency (TOF). Some superiorities of the introduced catalysts are their novelty, simple separation and their reusability up to six repeated runs without significant catalytic deactivation.