Brønsted acid catalyzed Prins-Ritter reaction for selective synthesis of terpenoid-derived 4-amidotetrahydropyran compounds

A number of SO3H-functionalized solids (biochar, montmorillonites, carbon and halloysite nanotubes) has been studied as catalysts in the cascade Prins-Ritter reaction (-)-isopulegol with benzaldehyde acetonitrile for synthesis octahydro-2H-chromene amides (as 4R- 4S-isomers). high selectivity to these products at 30 °C presence H2O was observed on modified chlorosulfonic acid (CSA) reaching 84% (4R/4S 5.7) case biochar, while a relatively large amount octahydro-2H-chromenols (up 31%), Prins condensation, formed materials functionalized by 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSP). Although condensation proceeds efficiently weak sites, requires sulfated strong (0.33 – 5.8 mmol/g) Brønsted acidity. Catalysts CSP were stable, acid, leaching -SO3H groups observed. Nonetheless, resistant Bioсhar-CSP, (67%) higher than that commercial Amberlyst-15 (47%), triflic − 25 (62%). Similar desired Biochar-CSA (-SO3H groups) H2SO4 (81–84%) well Biochar-CSP (-PhSO3H) p-toluenesulfonic (67–70%) DFT calculations experimental results showed formation 4S-amide thermodynamically is more beneficial alcohols dehydration products. However, addition water sharp increase rate 4R-amide due change kinetic control, leading eventually both yields stereoselectivity. The proposed pathways also confirmed modelling.