Prins cyclization: Synthesis of compounds with tetrahydropyran moiety over heterogeneous catalysts

Prins cyclisation of (–)-isopulegol with benzaldehyde over ZSM-5 based micro-mesoporous catalysts for production of pharmaceuticals

“…It is also important to note that 9MMAS possessing a very large amount of strong acid sites exhibits the initial rate which is only 32% of the initial rate for 5MMAS showing that a too high amount of strong acid sites is not favourable. These results were correlated with the initial rates obtained over different zeolites, mesoporous materials and metal modified zeolites by Stekrova et al [11], who concluded that too high amounts of strong acid sites, especially in Au-Beta-25, give lower initial rates than the parent zeolites and mildly acidic Ce-MCM-41. Noteworthy is that the initial rate for 4MMAS was very low, however, this material was very active already during heating of the reaction mixture.…”

“…It was also observed that octahydrochromane compound, with tetrahydropyran structure (compound 6 in Fig. 1), formed from (-)-isopulegol and benzaldehyde was further partially transformed to dioxinol type product 5 over Ce-modified mildly acidic MCM-41 composite material [11]. Dioxinol, being another valuable product from Prins cyclisation of (-)-isopulegol with benzaldehyde (Fig.…”

Sulfonated Hyper‐cross‐linked Porous Polyacetylene Networks as Versatile Heterogeneous Acid Catalysts

“…The DHP/THPol mole ratios were 7.3 and 3.8 with Amberlyst 15 and p ‐TSA, respectively, whereas both P(1,4‐DEB)‐SO 3 H and P(1,3‐DEB)‐SO 3 H provided the DHP/THPol ratio of about 1.4 (data corresponding to the conversion of benzaldehyde of 80 % are reported). The preference of formation of DHP can be caused by the acidity of used catalysts, which induced the dehydration reaction. The DHP isomers were preferred using all mentioned catalysts, the selectivity to DHP isomers was the highest using Amberlyst 15 (87 %) followed by p ‐TSA (72 %) compared to p(1,4‐DEB)‐SO 3 H (53 %) and p(1,3‐DEB)‐SO 3 H (54 %).…”

Acid‐modified Halloysite Nanotubes as a Stereoselective Catalyst for Synthesis of 2H‐Chromene Derivatives by the Reaction of Isopulegol with Aldehydes

“…Recently, it has been shown, that in catalytic condensation of a natural allyl alcohol (−)‐isopulegol (I) with aldehydes, substituted octahydro‐2 H ‐chromen‐4‐ol (III) as 4 R ‐ and 4 S ‐diastereomers was formed along with a dehydration product IV (Scheme ). Different catalysts such as I 2 , p ‐toluenesulfonic acid, BF 3 ⋅Et 2 O, zeolites, clays were used in this reaction . A relatively high 4 R /4 S ratio (9.0) with overall yields of 70–88 % were observed in condensation of isopulegol (obtained by cyclization of R ‐citronellal) with aromatic aldehydes at −78 °C using scandium triflate .…”