Catalytic synthesis of terpenoid-derived hexahydro-2H-chromenes with analgesic activity over halloysite nanotubes
[Display omitted] •First systematic study of catalytic terpenoid diol condensation with an aldehydes to bioactive hexahydro-2H-chromene-4,8-diols.•Halloysite nanocatalyst increases both the yields of hexahydro-2H-chromene-4,8-diols and 4S/4R isomers ratio.•Inversion of stereoselectivity with increas...
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Published in | Applied catalysis. A, General Vol. 618; p. 118144 |
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Main Authors | , , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Amsterdam
Elsevier B.V
25.05.2021
Elsevier Science SA |
Subjects | |
Online Access | Get full text |
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Summary: | [Display omitted]
•First systematic study of catalytic terpenoid diol condensation with an aldehydes to bioactive hexahydro-2H-chromene-4,8-diols.•Halloysite nanocatalyst increases both the yields of hexahydro-2H-chromene-4,8-diols and 4S/4R isomers ratio.•Inversion of stereoselectivity with increasing acidity or catalyst drying temperature.•The reaction mechanism is discussed with DFT calculations and kinetic modeling.
Condensation of α-pinene derived p-menta-1,8-diene-5,6-diol (diol) with decanal was studied for the first time over modified halloysite nanotubes (HNT). The yield of the desired hexahydro-2H-chromene-4,8-diol with analgesic activity was 76–80 % practically not depending on the catalyst type, while selectivity to 4S-isomer decreased, and to 4R-isomer increased with increasing acidity. The highest selectivity to 4S-diastereomer (48.1 %) on halloysite is a result of weak acidity of this catalyst. DFT optimization of the key intermediate structure shows that the nucleophile attack proceeds at the equatorial position with the 4S-diastereomer formation, which was preferred on halloysite. On strong Brønsted (Amberlyst-15) and Lewis (scandium triflate) acids the target product yield did not exceed 37 % because of dehydration. Halloysite nanocatalysts displayed a stable performance. In the case of diol reaction with a set of carbonyl compounds, the yields of hexahydro-2H-chromene-4,8-diols (up to 88.0%) and the ratio of its 4S/4R isomers (up to 21.0) were significantly higher than on other catalysts. |
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ISSN: | 0926-860X 1873-3875 |
DOI: | 10.1016/j.apcata.2021.118144 |