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Your search keyword '"Čejka J."' showing total 114 results
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114 results on '"Čejka J."'

19. One-pot synthesis of cyclohexylphenol via isopropyl alcohol-assisted phenol conversion using the tandem system RANEY® Nickel plus hierarchical Beta zeolite.

Author

García-Minguillán, A. M., Briones, L., Alonso-Doncel, M., Čejka, J., Serrano, D. P., Botas, J. A., and Escola, J. M.

Subjects
PHENOL, ZEOLITES, NICKEL, ISOPROPYL alcohol, LEWIS acids, UNIFORM spaces
Abstract

Cyclohexylphenols are valuable intermediate chemicals applied in the manufacture of dyes, resins, and pharmaceutical drugs. However, they are synthesized using raw chemicals derived from fossil fuels rather than sustainable sources (e.g., lignin-derived phenol). In this article, we report a one-pot synthesis of cyclohexylphenols via phenol-assisted conversion with isopropyl alcohol over the tandem catalytic system formed by RANEY® Nickel plus hierarchical Beta zeolite. Over this tandem catalytic system, cyclohexylphenols were synthesized with remarkable selectivity (∼70%) at high conversion rates (64%) after 1 h of reaction at 150° C. In contrast, higher temperatures (175 °C) were required to obtain alkylphenols over the Al-SBA-15 catalyst, which is highly accessible thanks to its uniform mesoporous structure, albeit with weaker Lewis acid sites. Additionally, selectivity to cyclohexylphenols over Al-SBA-15 was far lower (19%) than over hierarchical Beta zeolite, and cresols were instead the most abundant alkylphenol (26%). Therefore, the combination of suitable accessibility and Brønsted acidity of hierarchical Beta with the hydrogenating ability of RANEY® Ni through catalytic hydrogen transfer from isopropyl alcohol drives the selectivity of this tandem system towards the production of cyclohexylphenols. [ABSTRACT FROM AUTHOR]

Published
2022
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45. Inherent chirality through a simple dialkylation of 2,14-dithiacalix[4]arene.

Author

Kortus, D., Kundrát, O., Tlustý, M., Čejka, J., Dvořáková, H., and Lhoták, P.

Subjects
CHIRALITY, MITSUNOBU reaction, STEREOISOMERS, CALIXARENES, MIXTURES, CHIRALITY of nuclear particles
Abstract

The dialkylation of 2,14-dithiacalix[4]arene was studied employing various synthetic procedures known for the parent macrocycles (thiacalixarenes and/or classical calixarenes). The best results for distal dialkylation were achieved using the Mitsunobu reaction with the corresponding alcohols. Interestingly, due to the lower symmetry of the starting compound, the dialkylated derivatives represent inherently chiral systems. The introduction of chiral substituents thus leads to mixtures of diastereomers potentially useful for the separation of individual stereoisomers as demonstrated by chiral HPLC. The conformational behavior of the novel compounds was studied both in solution (NMR) and in the solid state (X-ray). [ABSTRACT FROM AUTHOR]

Published
2020
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46. Regioselective formation of the quinazoline moiety on the upper rim of calix[4]arene as a route to inherently chiral systems.

Author

Tlustý, M., Dvořáková, H., Čejka, J., Kohout, M., and Lhoták, P.

Subjects
RESOLUTION (Chemistry), SINGLE crystals, ATROPISOMERS, CYANIDES, CALIXARENES
Abstract

The meta- and para-substituted aminocalix[4]arenes immobilized in the cone conformation were acylated to yield the corresponding acyl amides. Subsequent cyclization with aryl or alkyl cyanides afforded the expected quinazolines only in the case of the para-substituted series, while only complex reaction mixtures were obtained for the meta-substituted analogues. This finding was used as a strategy for the preparation of novel inherently chiral calixarenes with strong fluorescence. The structure of the products was proved by the combination of NMR and single crystal X-ray analyses. The dynamic NMR study of quinazoline derivatives revealed the existence of two different atropisomers in solution at lower temperatures. As evidenced by resolution with a chiral HPLC column and by the fluorescence titration experiments, novel quinazolines represent inherently chiral macrocycles of high potential for the design of chiral calixarene-based receptors. [ABSTRACT FROM AUTHOR]

Published
2020
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