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

Abstract

Acid-modified halloysite nanotubes were used for the first time as a stereoselective catalyst for synthesis of oxygen-containing heterocycles applying of allyl alcohol (À)-isopulegol condensation with aldehydes to the octahydro-2H-chromenol (4R-and 4S-diastereomers) as an example. The catalysts were characterized by XRF, XRD, N 2 -adsorption, FTIR with pyridine and MAS NMR methods. A high ratio of 4R/4S diastereomers (7.6-14.5) under mild conditions in cyclohexane was considerably exceeding previously reported results. Unprecedented selectivity (79-83 %) to 4R isomer of thiophenyl-substituted chromenol exhibiting high analgesic activity was achieved. An increase in stereoselectivity with a decrease in the halloysite drying temperature and catalyst acidity clearly indicates formation of 4R diastereomer on the weak Brønsted sites. This work is an example that control of the stereoselectivity of acid-catalyzed organic reactions can be effectively carried out by varying water content on the aluminosilicate surface. Modified halloysite nanotubes can be considered as extremely promising catalysts for stereoselective synthesis of heterocyclic compounds.

A novel approach for preparation of nanocomposites with an excellent rigidity/deformability balance based on reinforced HDPE with halloysite

“…The amount of acid sites present in these HNT is much lower than those found in a synthesized batch of dendrimeric silica (DS) nanoparticles containing aluminum (Al) (DSAl materials), although in the present case a higher amount of Al compared with Si was found [32]. A similar acidity site concentration for halloysite was reported by Sidorenko et al [33] with a acid site concentration of 34 µmol/g, and a predominance of Lewis acid sites present.…”

Halloysite Nanotubes: Smart Nanomaterials in Catalysis

“…In another work, pristine HNTs pre-treated with HCl were successfully employed as catalyst in the condensation of an allyl alcohol isopulegol with aldehydes to obtained chromene-based molecules, which possess a broad spectrum of biological activity [54]. Different experimental conditions were considered, and the results showed that the reactions are strictly influenced by halloysite drying temperature (Table 2).…”

Enantiomeric Isopulegol as the Chiral Pool in the Total Synthesis of Bioactive Agents

“…The diastereoismer with (R) configuration at C-4 of substituted octahydro-2Hchromen-4-ol exhibits biological activity, while the S-diastereomer practically does not show any effect. [49] Besides homogenous Lewis catalysts such as I 2 (81 %, R/S = 5 : 1), [50] BF 3 • OEt 2 (60 %, R/S = 3 : 1), [51] Prins reaction between isopulegol and carbonyl compounds was also perfomed over heterogenous Lewis catalysts such as acid-activated montmorillonite (75.7 %, R/S = 5.3 : 1), [52,53] sulfonic acid modified K10 clay (73 %, R/S = 7.6 : 1) [49] or organosilylated sulfur containing K10 clay (90 %, R/S = 11.5 : 1), [54] acid-modified illite L-1 clay (81.7 %, R/S = 6.8 : 1), [55] halloysite nanotubes (77 %, R/S = 8.4 : 1), [56,57] acid-modified halloysite nanotubes (97 %, R/S = 6.6 : 1), [58] beta zeolites (93.3 %, R/S = 6.6 : 1), [59] Ce-MCM-41 (100 %, R/S mixture), [60] mesoporous Ce-composite (96 %, R/S mixture), [61] HCl-kaolin (90 %, R/S = 6.2 : 1) and HCl-metakaolin solids (86 %, R/S = 6.8 : 1) (Figure 1). [62,63] The first application of the octahydro-2H-chrome core, prepared in one step via the reaction of (À )-isopulegol 2 with different 2-thiophenecarboxaldehyde derivatives, against influenza A virus was reported by Nizamova et al in 2017.…”