共查询到20条相似文献,搜索用时 15 毫秒
1.
Ab Initio Study of Conformational Properties of ( Z, Z)-, ( E, Z)-, and ( E, E)-Cyclonona-1,5-dienes
Issa Yavari Rahebeh Amiri Mina Haghdadi 《Monatshefte für Chemie / Chemical Monthly》2004,135(8):937-950
Summary. Ab initio calculations at the HF/6-31G* level of theory for geometry optimization and MP2/6-31G*//HF/6-31G* for a single point total energy calculation are reported for the important energy-minimum conformations and transition-state geometries of (Z,Z)-, (E,Z)-, and (E,E)-cyclonona-1,5-dienes. The C2 symmetric chair conformation of (Z,Z)-cyclonona-1,5-diene is calculated to be the most stable form; the calculated energy barrier for ring inversion of the chair conformation via the Cs symmetric boat-chair geometry is 58.3kJmol–1. Interconversion between chair and twist-boat-chair (C1) conformations takes place via the twist (C1) as intermediate. The unsymmetrical twist conformation of (E,Z)-cyclonona-1,5-diene is the most stable form. Ring inversion of this conformation takes place via the unsymmetrical chair and boat-chair geometries. The calculated strain energy for this process is 63.5kJmol–1. The interconversion between twist and the boat-chair conformations can take place by swiveling of the trans double bond with respect to the cis double bond and requires 115.6kJmol–1. The most stable conformation of (E,E)-cyclonona-1,5-diene is the C2 symmetric twist-boat conformation of the crossed family, which is 5.3kJmol–1 more stable than the Cs symmetric chair–chair geometry of the parallel family. Interconversion of the crossed and parallel families can take place by swiveling of one of the double bonds and requires 142.0kJmol–1. 相似文献
2.
Ab Initio Study of Conformational Properties of ( Z, Z)-, ( E, Z)-, and ( E, E)-Cyclonona-1,5-dienes
Issa Yavari Rahebeh Amiri Mina Haghdadi 《Monatshefte für Chemie / Chemical Monthly》2004,44(5):937-950
Ab initio calculations at the HF/6-31G* level of theory for geometry optimization and MP2/6-31G*//HF/6-31G* for a single point total energy calculation are reported for the important energy-minimum conformations and transition-state geometries of (Z,Z)-, (E,Z)-, and (E,E)-cyclonona-1,5-dienes. The C2 symmetric chair conformation of (Z,Z)-cyclonona-1,5-diene is calculated to be the most stable form; the calculated energy barrier for ring inversion of the chair conformation via the Cs symmetric boat-chair geometry is 58.3kJmol–1. Interconversion between chair and twist-boat-chair (C1) conformations takes place via the twist (C1) as intermediate. The unsymmetrical twist conformation of (E,Z)-cyclonona-1,5-diene is the most stable form. Ring inversion of this conformation takes place via the unsymmetrical chair and boat-chair geometries. The calculated strain energy for this process is 63.5kJmol–1. The interconversion between twist and the boat-chair conformations can take place by swiveling of the trans double bond with respect to the cis double bond and requires 115.6kJmol–1. The most stable conformation of (E,E)-cyclonona-1,5-diene is the C2 symmetric twist-boat conformation of the crossed family, which is 5.3kJmol–1 more stable than the Cs symmetric chair–chair geometry of the parallel family. Interconversion of the crossed and parallel families can take place by swiveling of one of the double bonds and requires 142.0kJmol–1. 相似文献
3.
The first syntheses of the antitumor agents (E)-volkendousin (1) and acetonide 3 have been accomplished by efficient routes from readily available dehydroisoandrosterone (7) using allylic oxidation with SeO2 to introduce the 4/gb-hydroxy group and 16-ketone. This sequence should make these compounds readily available for further biological evaluation. 相似文献
4.
Vera L. M. Silva Artur M. S. Silva Diana C. G. A. Pinto José A. S. Cavaleiro Attila Vasas Tamás Patonay 《Monatshefte für Chemie / Chemical Monthly》2008,5(1):1307-1315
Several (E)- and (Z)-3-styrylchromones were prepared by two different methodologies, the Wittig reaction of chromone-3-carboxaldehyde with benzylic ylides and the Knoevenagel condensation of chromone-3-carboxaldehyde with phenylacetic acids in the presence of potassium tert-butoxide under microwave irradiation. The Knoevenagel reaction followed by a decarboxylation offered an efficient and diastereoselective method for preparing (E)-3-styrylchromones in a shorter reaction time. It was also demonstrated that phenylacetic acid can also be substituted with
success by phenylmalonic acid. The stereochemistry of all products was assigned by NMR experiments. 相似文献
5.
Vera M. Divac Marina D. Rvovi? Zorica M. Bugar?i? 《Monatshefte für Chemie / Chemical Monthly》2008,43(6):1373-1376
A fast and efficient method for intramolecular heterocyclization of (Z)- and (E)-hex-4-en-1-ols was developed. The method does not cause side reactions of the substrates and provides the cyclic phenylselenoethers
in high yields after only few minutes. A catalytic amount of SnCl2 increased the yield, but in the presence of an equimolar amount of SnCl2, formation of corresponding cyclic ethers were almost quantitative and reaction occurred instantaneously under extremely
mild experimental conditions. 相似文献
6.
N. V. Kovganko S. N. Sokolov Yu. G. Chernov A. V. Baranovskii 《Chemistry of Natural Compounds》2011,47(4):592-596
(Z)- and (E)-3-(2-chloropyridin-5-ylmethyl)oximino-(22E,24R)-ergosta-4,7,22-trienes (5–6) were synthesized by chemical transformation of ergosterol. Several oxidative transformations of them were studied. It was
found that oxidation of these compounds by chromium(VI) oxide formed the corresponding O-substituted 3-ketoximes of the mycosteroid (22E,24R)-ergosta-4,7,22-trien-3,6-dione (7) and (8), which contained α-chloropyridine fragments characteristic of biologically active neonicotinoids. It was shown that oxidation of 5 and 6 by selenium dioxide occurred with formation of the corresponding 9α-hydroxy derivatives 9 and 10. 相似文献
7.
Vera L. M. Silva Artur M. S. Silva Diana C. G. A. Pinto José A. S. Cavaleiro José Elguero 《Monatshefte für Chemie / Chemical Monthly》2009,45(2):87-95
Abstract
An efficient synthesis method for the preparation of a series of new (Z)- and (E)-3(5)-(2-hydroxyphenyl)-4-styrylpyrazoles was developed. The reaction of (Z)- and (E)-3-styrylchromones with hydrazine hydrate afforded the corresponding (Z)- and (E)-3(5)-(2-hydroxyphenyl)-4-styrylpyrazoles, except for nitro derivatives, where both (Z)- and (E)-4′-nitro-3-styrylchromones afforded (E)-3(5)-(2-hydroxyphenyl)-4-(4-nitrostyryl)pyrazoles. The reaction mechanism for these transformations is discussed and the stereochemistries of all products were established by NMR experiments. 相似文献8.
William A. Renters Gabriel J. Gibs Martin J. Weiss 《Journal of heterocyclic chemistry》1967,4(3):344-348
Treatment of ethyl 3-quinuclidinone-2-carboxyIate (III) with appropriate reagents gave 2,3-fused heterocycles including pyrazolol, aminopyrimidinone, and aminopyridazinone types. The thiourea derivative of III could not be cyclized. Triazoline, pyrazoline, and isoxazoline derivatives were prepared by 1,3-dipolar cycloadditions to the 2- and 3-positions of methyl 2,3-dehydroquinuclidine-3-carboxylate (XIIIa). Such facile formation of cycloaddition products was not possible with 2,3-dehydroquinuclidine, which reacted only with phenylazide (in poor yield). Structural assignments for the products of cycloaddition were made by analogy, but alternative structures could not be ruled out by the nmr or mass spectra. 相似文献
9.
Andrew G. McKillop Roger M. Smith Raymond C. Rowe Stephen A. C. Wren 《Journal of chromatography. A》1995,700(1-2):69-72
A mixture of the Z and E isomers of 2-(3-pentenyl)pyridine has been separated with baseline resolution by capillary electrophoresis. Using molecular modelling it was proposed that the smaller more rapidly migrating peak would be the Z isomer. This agreed with a 38:62 (Z/E) composition by nuclear magnetic resonance spectroscopy. The sample was also investigated by gas chromatography coupled to mass spectrometry. 相似文献
10.
G. G. Trigo M. Martinez E. Galvez R. Cabezas 《Journal of heterocyclic chemistry》1981,18(8):1507-1511
The synthesis of quinuclidine-3-spiro-5′-oxazolidine-2′,4′-dione, quinuclidine-3-spiro-5′-hydantoin, and some 3′-derivatives is described. Based on the data from 1H and 13C-nmr spectra the structure of the above mentioned compounds is established. A relationship between second order effects in 13C-nmr spectra and H-C-C-H dihedral angles is deduced. 相似文献
11.
12.
13.
Mechanisms of syn-(Z)/anti-(E) isomerization of methyl 2-methoxy-N-methylbuta-2,3-dienimidothioate, including rotational, inversion, promoted by N-protonation, and nucleophile-catalyzed, were
studied by quantum-chemical methods, and the corresponding thermodynamic and kinetic parameters were calculated. The most
probable mechanisms of isomerization of buta-2,3-dienimidothioates were found to be inversion (E
a = 74.4 kJ/mol) and nucleophile-catalyzed (E
a = 61.6 kJ/mol).
Original Russian Text ? V.A. Shagun, N.A. Nedolya, 2007, published in Zhurnal Organicheskoi Khimii, 2007, Vol. 43, No. 11,
pp. 1591–1600.
For communication XII, see [1]. 相似文献
14.
Reduction of a (bisphenyl)dithioacetal with sodium/isopropyl alcohol in THF allows preparation of (2E,6E)-10,11 -dihydrofarnesol in high yield. 相似文献
15.
Krzysztof Waskiewicz Rafal Gabanski Radoslaw Motyka Mieczyslaw Lapkowski Jerzy Suwinski Jerzy Zak 《Journal of Electroanalytical Chemistry》2008,617(1):27-37
The group of 1,4-dialkoxy-2,5-bis[2-(thien-2-yl)ethenyl]benzene stereoisomers was synthesized in which methoxy- and ethoxy-groups were used as alkoxy-substituents. These isomers were characterized as solution species both electrochemically and spectroscopically. As expected, these compounds, having a stilben like structure, are the subject of photoisomerization, which is described and discussed. It is demonstrated how electrochemical process may cause isomerization of the double CC bonds in that group of compounds. An attempt of using electrochemical methods to monitor the process of photoisomerization of these compounds is presented. Mechanism of the oxidatively induced electrochemical isomerization has been proposed and discussed. The electrochemical isomerization mechanism is verified by digital simulation, which allowed estimating basic kinetic parameters of the processes. 相似文献
16.
I. S. Afonkin A. M. Sotnikov R. R. Gataullin L. V. Spirikhin I. B. Abdrakhmanov 《Russian Journal of Organic Chemistry》2004,40(12):1764-1768
Isomerization of 2-allyl-6-methylaniline by the action of potassium hydroxide at 300°C afforded cis and trans isomers of 2-methyl-6-(1-propenyl)aniline which were converted into the corresponding carbamates by treatment with ethyl chloroformate. Ethyl 2-methyl-6-(1-propenyl)phenylcarbamates reacted with bromine to give mixtures of 4-(1-bromoethyl)-8-methyl-1,4-dihydro-2H-3,1-benzoxazin-2-one and ethyl 2- methyl-6-(1,2-dibromopropyl)phenylcarbamates. Treatment of the same compounds with N-bromosuccinimide resulted in formation of 2-ethoxy-4H-3,1-benzoxazine derivatives. The reaction of N-{6-methyl-2-[(Z)- 1-propenyl]-phenyl}methanesulfonamide gave a mixture of stereoisomeric N-[6-methyl-2- (1,2-dibromopropyl)-phenyl]-methanesulfonamides.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 12, 2004, pp. 1815–1818.Original Russian Text Copyright © 2004 by Afonkin, Sotnikov, Gataullin, Spirikhin, Abdrakhmanov.For communication V, see [1]. 相似文献
17.
Yu. N. Sheinker E. M. Peresleni I. V. Persianova E. E. Mikhlina V. Ya. Vorob'eva A. D. Yanina L. N. Yakhontov 《Chemistry of Heterocyclic Compounds》1972,8(2):205-209
The tautomerism of 2-ethoxycarbonyl-3-oxoquinuclidine and 2-ethoxycarbonyl-3-oxobenzo-[b]quinuclidine was investigated by means of IR and UV spectra and potentiometric titration. It was found that tautomeric equilibrium between the ketone, enol, and internally ionized forms is realized for 2-ethoxycarbonyl-3-oxoquinuclidine, and the position of the equilibrium is determined by the aggregate state of the substance and the nature of the solvent. The internally ionized form predominates in the crystals and in polar solvents (alcohol and water), while the ketone and enol forms are the primary ones in solvents of low polarity (chloroform and dioxane), and the percentage of the ketone form is always larger than that of the enol form. In contrast to this, 2-ethoxycarbonyl-3-oxobenzo[b]quinuclidine exists practically completely as the keto form in crystals and solutions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 229–233, February, 1972. 相似文献
18.
Asymmetric hydroboration of [E]- and [Z]-2-methoxy-2-butene, using (−)-diisopinocampheylborane at −25°C in THF solvent, followed by oxidation using H2O2/NaOH, gave (−)-[2R,3R]- and (+)-[2R,3S]-3-methoxy-2-butanols in >97 and 90% ee, respectively. (−)-[2R,3R]-3-Methoxy-2-butanol was converted to (−)-[2R,3R]-butane-2,3-diol (>97% ee, in an overall yield of 65%). 相似文献
19.
A chiral HWE reagent reacted with an alternative carbonyl group of meso-α-diketones of bicyclo[2.2.1] system to give non-racemic (Z)- and (E)-olefins, respectively. 相似文献