Sc(OTf)3-catalyzed one-pot ene-Prins cyclization: a novel synthesis of octahydro-2H-chromen-4-ols

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

“…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 . The isomeric ratio was significantly lower (4.0) for aliphatic aldehydes as reactant .…”

“…It is known that compounds with a chromene (benzopyran) scaffold have a broad spectrum of biological activity . A high pharmaceutical potential and low toxicity of these substances resulted in a considerable interest in the synthesis of new chromene derivatives . 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 ).…”

“…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 .…”

“…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 . The isomeric ratio was significantly lower (4.0) for aliphatic aldehydes as reactant . In the presence of traditional Lewis acids (ZnCl 2 , FeCl 3 , AlCl 3 ) rather low yields of chromenols (12–48 %) were observed …”

Effect of structure and acidity of acid modified clay materials on synthesis of octahydro-2H-chromen-4-ol from vanillin and isopulegol

“…Recently, acid-activated natural clays were suggested as catalysts for such type of reaction. Thus, octahydro-2H-chromen-4-ols with good yields were synthesized from (−)-isopulegol and various types of aldehydes in the presence of montmorillonites K10 [3] and KSF [4] modified by H 2 SO 4 . In our previous work [5], we also demonstrated the possibility of application of two montmorillonites from beds located in Mukhortala (Buryatia, Russia) and Tagansk (Kazakhstan) modified by 0.125-3.0 mol/dm 3 HCl for the Prins cyclization of (−)-isopulegol (I) with vanillin (II) to form octahydro-2H-chromen-4-ol (III) (Reaction 1).…”