Prins cyclization in 4-methyl-2-phenyl-tetrahydro-2H-pyran-4-ol preparation using smectite clay as catalyst

Florol synthesis via Prins cyclization over hierarchical beta zeolites

“…Solid-state 29 Si MAS NMR and 27 Al MAS NMR spectra were obtained using an Avance III HD (Bruker) spectrometer working with a 9.4 T standard-bore superconducting magnet at resonance frequency 79.5 MHz and 104.26 MHz, respectively. The samples were packed into a thin-wall 3.2 mm zirconia rotor, and rotated at a MAS rate of 15 kHz using a Bruker 3.2 mm HX CP-MAS probe.…”

“…The samples were packed into a thin-wall 3.2 mm zirconia rotor, and rotated at a MAS rate of 15 kHz using a Bruker 3.2 mm HX CP-MAS probe. For recording 29 Si MAS NMR spectrum, a pulse of 1.9 μs (ca. 60 • flip angle) with a relaxation delay of 20 s was applied and 2500 transients were averaged.…”

“…The local environment of the Si and Al atoms in the representative sample HBZ-3 was investigated by using 29 Si MAS NMR and 27 Al MAS NMR spectroscopy, respectively. The peak at -100 ppm in the 29 Si MAS NMR spectrum of this sample (Fig.…”

“…At the same time modification of zeolites, namely Beta, with iron is accompanied with an increase in conversion of the initial reagents (benzaldehyde or butanal in the reaction with isoprenol) while selectivity toward the reaction products (tetrahydropyranols, dihydropyrans and acetals) was almost unchanged [28]. Prins cyclisation of isoprenol with several aldehydes was also studied over montmorillonite K10 showing for isovaleraldehyde, in particular, 61% selectivity towards the desired substituted tetrahydropyranol at 95% conversion at 70 • C in toluene [29]. Acid-modified clays such as halloysite, montmorillonite and illite were also found to be promising for cyclization of isoprenol with isovaleraldehyde providing 65 -72% yield of tetrahydropyranol under solvent-free conditions [30].…”

Acid Treated Montmorillonite—Eco-Friendly Clay as Catalyst in Carvone Isomerization to Carvacrol

“…The positive effect on the acidity of montmorillonite caused by the acid treatment is widely discussed. Treatment with acid causes the exchange of some Na + ions from montmorillonite with H + from acid, which causes material acidity enhancement [19,20]. Acid treated montmorillonite was successfully used as catalyst in a wide range of reaction, e.g., α-terpineol synthesis from α-pinene [20], Prins reaction of benzaldehyde and isoprenol [19], Prins reaction of vanillin with isopulegol [21], methanol dehydration [22], benzene alkylation [22], production of fatty acid methyl esters [23,24] or Knovenagel condensation [25].…”