- Controlling the Conformational Energy of a Phenyl Group by Tuning the Strength of a Nonclassical CH···O Hydrogen Bond: The Case of 5-Phenyl-1,3-dioxane
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Anancomeric 5-phenyl-1,3-dioxanes provide a unique opportunity to study factors that control conformation. Whereas one might expect an axial phenyl group at C(5) of 1,3-dioxane to adopt a conformation similar to that in axial phenylcyclohexane, a series of studies including X-ray crystallography, NOE measurements, and DFT calculations demonstrate that the phenyl prefers to lie over the dioxane ring in order to position an ortho-hydrogen to participate in a stabilizing, nonclassical CH···O hydrogen bond with a ring oxygen of the dioxane. Acid-catalyzed equilibration of a series of anancomeric 2-tert-butyl-5-aryl-1,3-dioxane isomers demonstrates that remote substituents on the phenyl ring affect the conformational energy of a 5-aryl-1,3-dioxane: electron-withdrawing substituents decrease the conformational energy of the aryl group, while electron-donating substituents increase the conformational energy of the group. This effect is correlated in a very linear way to Hammett substituent parameters. In short, the strength of the CH···O hydrogen bond may be tuned in a predictable way in response to the electron-withdrawing or electron-donating ability of substituents positioned remotely on the aryl ring. This effect may be profound: a 3,5-bis-CF3 phenyl group at C(5) in 1,3-dioxane displays a pronounced preference for the axial orientation. The results are relevant to broader conformational issues involving heterocyclic systems bearing aryl substituents.
- Bailey, William F.,Lambert, Kyle M.,Stempel, Zachary D.,Wiberg, Kenneth B.,Mercado, Brandon Q.
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p. 12116 - 12127
(2016/12/23)
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- Enzyme catalysed asymmetrization of pyridyl substituted 1,3-propanediols and of the corresponding diacetates
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2-(4-pyridyl)- and 2-(2-pyridyl)-1,3-propanediols 1 and 4 were prepared and asymmetrized by enantioselective acetylation in organic solvent catalysed by hydrolytic enzymes, the best being supported pig pancreatic lipase, to give new valuable heterocyclic chiral building blocks. The asymmetrization of the diacetate 6, catalysed by pig pancreatic lipase is also described.
- Guanti, Giuseppe,Narisano, Enrica,Riva, Renata
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p. 2175 - 2187
(2007/10/03)
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- Synthesis and Biological Activity of 1,2-Dithiolanes and 1,2-Dithianes Bearing a Nitrogen-containing Substituent
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A series of 1,2-dithiolanes, 1,2-dithianes and related compounds bearing a nitrogen-containing substituent were synthesized and their pesticidal activity was tested.A new general synthetic route to 1,2-dithiolanes was established from 1,3-diols.A variation in the position and character of the nitrogen atom is shown to be allowable to some extent for promoting insecticidal activity, unlike the case of sulfur atoms.Most compounds showed acaricidal activity, the strongest being displayed by cis-3,5-bis(dimethylaminomethyl)-1,2-dithiolane.
- Uneme, Hideki,Mitsudera, Hiroyuki,Kamikado, Toshiya,Kono, Yoshiaki,Manabe, Yukiaki,Numata, Mitsuo
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p. 2023 - 2033
(2007/10/02)
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