Prins cyclization for the preparation of 2-isobutyl-4-methyl-tetrahydro-<Emphasis Type="Italic">2H</Emphasis>-pyran-4-ol using supported heteropoly acids

The selective preparation of 2-isobutyl-4-methyl-tetrahydro-2H-pyran-4-ol (also called Florosa or Florol) was performed. Prins cyclization of isoprenol and isovaleraldehyde was used for the preparation of this important fragrant compound. Heteropoly acids (phosphotungstic and phosphomolybdic) were used as a catalyst in homogeneous and also in heterogeneous arrangements (after their immobilization). The only solvent necessary for the reaction was water that enables the increase of the selectivity to the desired product by hydrolysis of catalyst-carbocation intermediates. In a flow, both heteropoly acids were successfully anchored on siliceous MCM-41 and resultant materials were characterized by XRF, XRD, SEM, FTIR, UV–Vis, and nitrogen adsorption. Heterogenization was performed in water as a solvent. Anchored heteropoly acids were used in Prins cyclization under the same conditions (addition of water), and the selectivity was even higher (96 %), comparing the homogeneous arrangement. No leaching of catalyst from solid was observed. Moreover, the catalyst may be reused without loss of activity and selectivity at least four times.