共查询到20条相似文献,搜索用时 171 毫秒
1.
L.J. Goad F.-X. Garneau J.-L. Simard J.W. ApSimon M. Girard 《Tetrahedron letters》1985,26(29):3513-3516
- 14α-Methyl-5α-cholest-9(11)-en-3β-ol () and 4α,14α-dimethyl-5α-cholest-9(11)-en-3β-ol () have been isolated from the sea cucumber and characterised by 1H NMR, 13C NMR and mass spectrometry. Lanost-9(11)-en-3β-ol () has also been tentatively identified. The relevance of this series of Δ9(11)-sterols to holothurin biosynthesis is briefly discussed. 相似文献
2.
J.L. Breton F. Camps J. Coll L. Eguren J.A. Gavin A.G. Gonzalez X. Martorell C. Miravitlles E. Molins J. Torramilans 《Tetrahedron》1985,41(15):3141-3146
A new heliangolide has been isolated from aerial parts of , and identified as (6,10)(3,3a,4,lla)-3a,5,8,11a--tetrahydro-4-acetoxy-3,6, 1O-trimethyl-2,9 (3, 4) -cyclodeca[b] furandione. The structural elucidation of the new compound, named heliangolidin, was carried out by spectral means (MS, IR, 1H and 13C NMR, and two dimensional 1H-13C chemical shift correlations) and X-ray diffraction analysis. 相似文献
3.
Tomas Fex 《Tetrahedron letters》1981,22(28):2703-2706
The structures of cytochalasin K, L and M, isolated from the fungus , have been determined by spectroscopic methods, primarily 1H NMR and 13C NMR. 相似文献
4.
Jan A. Glinski Balawant S. Joshi Szu-yinq Chen S.William Pelletier 《Tetrahedron letters》1984,25(12):1211-1214
A novel C19-diterpenoid alkaloid designated as tatsinine has been isolated from the roots of and its structure (3) has been derived from 1H NMR and 13C NMR spectroscopic evidence. 相似文献
5.
The conformation of several -2,3-diaryloxy-1,4-dioxanes has been studied using 1H NMR techniques. -2,3-bis(4-nitrophenoxy)-1,4-dioxane and -2,3-bis(4-methoxyphenoxy)-1,4-dioxane have been found to be predominantly ( ≈98%) in diaxial conformation in CDCl3). On the other hand, -2,3-bis(2,6-dimethylphenoxy)-1,4-dioxane exists in the same conditions as a 66:33 mixture of diaxial and diequatorial conformers. An explanation based on the fulfilment of the exo-anomeric effect is provided. 相似文献
6.
Using known NMR and structural data of solid silicates the linear correlation = 1.14 - 2014 between the isotropic 29Si NMR chemical shifts (ppm) and the “isotropic” mean bond lengths (nm) has been established. The results of semi-empirical calculations are in good agreement with this equation. 相似文献
7.
Kenichi Takeuchi Toshikazu Kitagawa Akihiko Ueda Yoshihide Senzaki Kunio Okamoto 《Tetrahedron》1985,41(23):5455-5463
7-Cyano-7-methylcycloheptatrienes containing one t-butyl group on the 1-position () or two t-butyl groups on the 1- and 3-, 1- and 4-, or 1- and 5-positions (, , or , respectively) were synthesized and their cyclo- heptatriene (CHT)-norcaradiene (NCD) equilibria measured by variable-temperature 1H NMR for CS2-CD2Cl2 solutions. The 1H NMR chemical shifts of the 7-methyl group indicate that these compounds are composed of essentially one CHT and one NCD tautomer with an endo geometry of the methyl group. The introduction of a t-butyl group at the 1-position of 7-cyano-7-methylcycloheptatriene () markedly shifts the equilibrium to the NCD side and the addition of the second t-butyl group further favors the NCD form, with the NCD populations for , , , and at 25 °C 70.9, 96.5, 92.3, and 99.3%, respectively. An application of molecular mechanics (MMPI) calculations to various t-butylated CHT-NCD systems suggests that the t-butyl groups sterically destabilize the CHT form more than the NCD form, bringing about increased NCD populations. 相似文献
8.
Condensation of 1,3-bis(trimethylsiloxy)-1-methoxybutadiene () and 2-phenyl-2,2-dimethoxyethanal () under TiCl4 condition gave the γ-hydroxycyclopentenone product . The reaction was followed by INEPT29Si NMR. Implication to the mechanism of the reaction was discussed. 相似文献
9.
Structural assignments of all possible diastereoisomers of 1-chloro- 2-ethoxy-1-fluoro-alkylcyclopropanes have been achieved through their 19F NMR spectra. The previously unreported effect of an ethoxyl group on the fluorine signal has been studied and found to promote in most cases a shielding effect in the vicinal -fluorine and a deshielding effect when to this halogen. 相似文献
10.
Hideshi Nakamura Houming Wu Junichi Kobayashi Yoichi Nakamura Yasushi Ohizumi Yoshimasa Hirata 《Tetrahedron letters》1985,26(37):4517-4520
Purealin , a novel secondary metabolite, which modurates enzymic reactions of ATPases, has been isolated from the okinawan marine sponge and the structure has been determined by the 1H-1H homonuclear and 1H-13C heteronuclear NMR chemical shift correlations and CD spectra. 相似文献
11.
Several π-excessive heteropolyaromatic compounds, which contain furan and thiophen ring and are possible antifungal agents, have been synthesized in good yields according to two general methods. The first method has been used to prepare compounds possessing thiophens linked by their 2- and 5-positions, such as the ter-aryls , and . Two precursors of these compounds have been obtained either by the Glaser reaction, or using a novel Pd-mediated reaction. The second method,which consists of the Ni-or Pd-catalyzed heteroarylation of heteroarene halides via cross-coupling with heteroaryl Grignard reagents or zinc halides,has been used to prepare the bi-aryls , which contain two heteroaromatic units, and the ter-aryl . Compound has been also prepared starting from 2-(2-thienyl) furan () by selective lithiation, followed by bromination.The 13C NMR signals of and have been assigned on the basis of the literature data and by relaxation measurements. Relaxation data have been also used to obtain qualitative informations on the conformational equilibria of the bi-aryls , and the ter-aryls . 相似文献
12.
The nucleophilic substitution reactions of some simple fluorobenzenes, C6H6?xFx with sodium methanethiolates Na+SR?(R=Et, -Pr, -Bu) have been studied. Some fully substituted products, C6H6?x(SR)x, could be obtained in DMF as solvent with R = Et and -Pr, but not when R = -Bu. All the new products isolated have been characterized by elemental analysis, and NMR (H-1 and F-19), infrared and mass spectroscopy. 相似文献
13.
Perfluoro--propylbromine(V) tetrafluoride has been prepared by fluorination of perfluoro--propyl bromide at 0°C with elemental fluorine. It has been characterized by 19FNMR, mass spectroscopy and elemental analysis. 相似文献
14.
The cycloaddition reactions of 6-oxo (2H) cyclohepta (c) pyrroles with diethyl acetylene dicarboxylate an electron-deficient dienophile of relatively low LUMO energy level, afford the 1:2 adducts respectively The kinetics of the reactions, investigated By 1H NMR spectroscopy, have allowed to precise the mechanism of the addition In particular, new-intermediates, 1:2' adducts have been observed and isolated for the compound . 相似文献
15.
Francis Pochat 《Tetrahedron letters》1979,20(32):2991-2994
Reaction of hydrazine with bromoderivatives , obtained from aldehydes, gives almost quantitatively 3(5)-aminopyrazoles . An approach of the structure of is attempted by 13C NMR. 相似文献
16.
Reaction of -(Gly--Cys-Gly)3 with 1,3,5--bromomethylbenzene yields a thioether of the cyclic nonapeptide in 28% yield. Both 1H and 13C NMR spectra are consistent with a molecule of 3-fold symmetry; the temperature dependences of chemical shifts of the amide hydrogens are consistent with a structure composed of three β-turns. 相似文献
17.
Three different types of butanolide complexes with EtnAlCl3?n in the molar ratios and have been investigated by IR with 1M NMR spectroscopy. The butanolides form and complexes with ethylaluminium halides, but with triethylaluminium only complexes are formed. The complexes are intermediates in the cleavage of butanolides. 相似文献
18.
The unsaturated ketones 1 – 10 were protonated at low temperatures and studied by dynamic 13C NMR spectroscopy. Four interconverting stereoisomers were detected which differ in their conformation with respect to the CO and CC (enone) single bond. 相似文献
19.
Dialkylcarbodiimides, , react with iminium salts, , to afford the formal 1,1-diaminosubstituted 2-azaallenium salts . According to dynamic NMR measurements compounds must be regarded as alkylidene-guanidinium salts , undergoing a fast topomerization via a transition state with allene geometry (2G=265 = 45.9 ± 1 kJmol-1 for ) and a slower rotation around the peripheral C-N bonds (transition state ; 2G=290= 58.0 ± 1 kJmol-1 for ). 相似文献
20.
1H NMR spectra of 1-alkyl-1,2,3,4-tetrahydro-2-oxo-3-azocinecarboxylates and -carbonitriles indicated that the geminal protons at the 1-α-position were located in noneqnivalent magnetic environments. The difference in the chemical shifts amounted to as much as 0.73 ppm in the case of methyl 1-ethyl-1,2,3,4-tetrahydro-2-oxo-3-azocinecarboxylate at 26°, and the free energy of activation for the coalescence was estimated to be larger than 23 . The same type of nonequivalence and coalescence phenomena were also observed even with dimethyl protons at the 1-γ-position of 1-isobutyl-1,2,3,4-tetrahydro-2-oxo-3-azocinecarboxylate (ΔG≠c = 19 ). The situation was hardly affected by the reduction of the CC double bonds. The nonequivalence was not observed, however, if the substituent at the 3-position was absent. Therefore, these novel 1H NMR spectra of 1-alkyl protons in the title compounds were concluded to be due to strong coupling between the restricted rotation around N(1)—C(α) bond and inversion of the 2-oxoazocine ring which required high energy of activation. 相似文献