A practical way to synthesize chiral fluoro-containing polyhydro-2H-chromenes from monoterpenoids

Abstract Conditions enabling the single-step preparative synthesis of chiral 4-fluoropolyhydro-2H-chromenes in good yields through a reaction between monoterpenoid alcohols with para-menthane skeleton and aldehydes were developed for the first time. The BF 3 ·Et 2 O/ H 2 O system is used both as a catalyst and as a fluorine source. The reaction can involve aliphatic aldehydes as well as aromatic aldehydes containing various acceptor and donor substituents. 4-Hydroxyhexahydro-2H-chromenes were demonstrated to be capable of converting to 4-fluorohexahydro-2H-chromenes under the developed conditions, the reaction occurs with inversion of configuration. 64

Synthesis of octahydro-2H-chromen-4-ol from vanillin and isopulegol over acid modified montmorillonite clays: Effect of acidity on the Prins cyclization

Two calcium-rich natural layered aluminosilicates containing 90–95 wt.% montmorillonite were chemically activated using 0.125–3.0 M HCl solutions. Structural and textural properties were characterized by X-ray diffraction, elemental analysis and N2-adsorption/desorption analyses. According to infrared spectroscopy using pyridine as probe molecule, the amount of Brønsted acid sites increased when increasing HCl concentration. The catalytic performance of these materials was investigated in the Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2H-chromen-4-ol, carried out in toluene at 35 °C. It was found that the amount of Brønsted acid sites and the microporosity of the catalysts are key factors for the control of the reaction rate and the selectivity towards octahydro-2H-chromen-4-o

A practical way to synthesize chiral fluoro-containing polyhydro-2H-chromenes from monoterpenoids

Conditions enabling the single-step preparative synthesis of chiral 4-fluoropolyhydro-2H-chromenes in good yields through a reaction between monoterpenoid alcohols with para-menthane skeleton and aldehydes were developed for the first time. The BF3·Et2O/H2O system is used both as a catalyst and as a fluorine source. The reaction can involve aliphatic aldehydes as well as aromatic aldehydes containing various acceptor and donor substituents. 4-Hydroxyhexahydro-2H-chromenes were demonstrated to be capable of converting to 4-fluorohexahydro-2H-chromenes under the developed conditions, the reaction occurs with inversion of configuration

Effect of acid modification of kaolin and metakaolin on Brønsted acidity and catalytic properties in the synthesis of octahydro-2H-chromen-4-ol from vanillin and isopulegol

Natural kaolin and the metakaolin obtained by calcination of kaolin at 650 °C were chemically activated using 0.25–3.0 mol/dm3 HCl solutions. Structural and textural properties of samples were characterized by X-ray diffraction, elemental analysis and N2-adsorption/desorption analyses. The amount of Brønsted acid sites (BAS) was determined by infrared spectroscopy using pyridine as probe molecule. The amount of BAS for kaolin rose with increasing HCl concentration up to 1.0 M, and decreased for higher concentrations, that is related with the leaching of Al from the solid. Effect of HCl concentration on amount of BAS was negligible for metakaolin. The catalytic performance of these materials was investigated in the Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2H-chromen-4-ol, carried out in toluene at 50 °C. The reaction rate and the selectivity toward octahydro-2H-chromen-4-ol depended on the Bronsted acidity, structural and textural properties of the catalysts. The reaction rate in the presence of kaolin modified by HCl correlated with the amount of BAS. HCl-kaolin samples were more active compared with HCl-metakaolin, while selectivity reaction toward octahydro-2H-chromen-4-ol was larger in the presence of HCl-metakaoli