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1.
2.
Sammelson RE Gurusinghe CD Kurth JM Olmstead MM Kurth MJ 《The Journal of organic chemistry》2002,67(3):876-882
An efficient and selective method for the synthesis of spiro-fused (C5)-isoxazolino-(C4)-pyrazolones (C) is reported. The process consists of utilizing the Baylis-Hillman reaction-or a quicker, stepwise MAC procedure-to give I followed by 1,3-dipolar cycloaddition and Swern oxidation to give beta-ketoesters H, which were condensed with hydrazine derivatives to provide hydrazones that underwent cycloelimination. These novel spiro-fused (C5)-isoxazolino-(C4)-pyrazolones were confirmed by spectroscopic analysis as well as single-crystal X-ray of 5. We also concluded that all condensations/cycloeliminations, except with hydrazine itself, were more effective with catalysts or higher reaction temperatures. For example, TiCl(4) was an efficient catalyst for hydrazone formation and cycloelimination with methylhydrazine, while phenyl-, benzyl-, and (4-methoxyphenyl)hydrazine reacted effectively without catalyst in refluxing xylene. 相似文献
3.
Wolfgang Oppolzer Mark Kurth Daniel Reichlin Frank Moffatt 《Tetrahedron letters》1981,22(27):2545-2548
The chiral induction in the Diels-Alder addition → , assessed reliably by 19F-NMR-spectroscopy of the endo-esters , varied between 47 - 93% in favor of the 2-(R)-adducts depending on the auxiliary chiral group and the Lewis-acid catalyst. 相似文献
4.
The intramolecular Diels-Alder (IMDA) reactions of C(8)-substituted decatrienoates have been studied. The stereospecific formation of 11 via an endo-boat-9 transition state attests to the powerful directing influence of a C(8) substituent in the IMDA of decatrienoate. In addition, the contrasting observations that stereospecific 9 --> 11 occurs at room temperature while the nor-tert-butyl substrate (4a) requires 125 degrees C/5 h reaction conditions and produces a 60:40 mixture of diastereomers provide clear evidence that a bulky C(8) substituent is a powerful conformational activator of the IMDA. 相似文献
5.
W. Lautsch W. Broser W. Bandel W. Biedermann W. Gehrmann E. Schröder H. Gnichtel I. Zehmisch G. Kurth R. Krüger H. J. Kraege 《Colloid and polymer science》1954,138(3):129-142
Ohne Zusammenfassung
Die Arbeit wurde aus Mitteln des Marshall-Planes (ERP-Mittel) und mit Spenden aus dem „Fonds Chemie“ ausgeführt. Wir sprechen
den zust?ndigen Stellen für die Gew?hrung der Beihilfe unseren verbindlichsten Dank aus. Der Deutschen Forschungsgemeinschaft
danken wir für die überlassung einer Ultrazentrifuge, den Behring-Werken für die uns zur Verfügung gestellten Serumalbumin-
und -globulin-Pr?parate. 相似文献
6.
Polyoxometalates (POMs) comprise a structurally diverse class of inorganic transition metal oxygen clusters which—owing to their unique electronic properties—hold promise for a host of technological applications such as electrochromic windows, sensors, or heterogeneous catalysts, prototypic examples of which will be briefly exemplified. The integration of POMs into functional architectures and devices, however, necessitates the development of general methods that allow positioning these clusters in well-defined supramolecular architectures, thin films, or mesophases. This short review highlights recent advances in the preparation of composite multilayers fabricated by electrostatic layer-by-layer self-assembly (ELSA) of POMs and a variety of water-soluble cationic species, including transition metal complexes, cationic surfactants, polycations and bipolar pyridine. 相似文献
7.
Volkmer D Bredenkötter B Tellenbröker J Kögerler P Kurth DG Lehmann P Schnablegger H Schwahn D Piepenbrink M Krebs B 《Journal of the American Chemical Society》2002,124(35):10489-10496
Combining analytical and theoretical methods, we present a detailed study of a heteropolytungstate cluster encapsulated in a shell of dendritically branching surfactants, namely (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], 3. This novel surfactant-encapsulated cluster (SEC) self-assembles spontaneously from polyoxometalate-containing solutions treated with a stoichiometric amount of dendrons. Compound 3 exhibits a discrete supramolecular architecture in which a single polyoxometalate anion resides in a compact shell of dendrons. Our approach attempts to combine the catalytic activity of polyoxometalates with the steric properties of tailored dendritic surfactants into size-selective catalytic systems. The structural characterization of the SEC is based on analytical ultracentrifugation (AUC) and small-angle neutron scattering (SANS). The packing arrangement of dendrons at the cluster surface is gleaned from molecular dynamics (MD) simulations, which suggests a highly porous shell structure due to the dynamic formation of internal clefts and cavities. From analysis of the MD trajectory of 3, a theoretical neutron-scattering function is derived that is in good agreement with experimental SANS data. Force field parameters used in MD simulations are partially derived from a quantum mechanical geometry optimization of [(Zn(H(2)O))(3)(SbW(9)O(33))(2)](12)(-), 2b, at the density functional theory (DFT) level. DFT calculations are corroborated by X-ray structure analysis of Na(6)K(6)[(Zn(H(2)O))(3)(SbW(9)O(33))(2)].23H(2)O, which is isostructural with the catalytically active Mn derivative 2a. The combined use of theoretical and analytical methods aims at rapidly prototyping smart catalysts ("dendrizymes"), which are structurally related to naturally occurring metalloproteins. 相似文献
8.
9.
The syntheses, structures, and spectroscopy of a series of oligomeric tertiary oligophenylureas possessing one to five phenyl rings are reported. A convergent synthetic method employing tertiary monoamine and diamine building blocks is employed. NMR and molecular modeling are indicative of folded structures for all of the oligophenylureas in which adjacent phenyl rings have a splayed face-to-face geometry. NMR chemical shifts, absorption and emission maxima, and electrochemical oxidation potentials are all dependent upon the number of phenyl rings. The addition of a first inner phenyl has a pronounced effect on the chemical shifts, while a second and third inner phenyl have diminished effects. The oxidation potentials of the oligophenylureas display an abrupt decrease upon the addition of the second inner phenyl. The absorption and emission spectra are relatively insensitive to the addition of one to three inner phenyl rings. The electronic structures of the oligophenylureas possessing one to eight rings have been analyzed using ZINDO calculations. The frontier orbitals of the ureas with one to three phenyl rings are localized on a single phenyl ring (the inner ring for the three-ring urea), whereas the frontier orbitals of the higher oligomers are delocalized over two phenyl rings. In all cases, urea-localized n,pi* transitions are lower in energy than the phenyl-localized pi,pi* transitions. The changes in properties with added phenyl rings parallel those previously observed for multilayered cyclophanes; however, they are less pronounced because of weaker coupling between the phenyl rings of the oligophenylureas. 相似文献
10.
A study of structural modifications of MPB-07 was undertaken as part of a synthetic program aimed at discovering small molecules with CFTR activation potential. Solid-phase synthesis techniques were used to prepare derivatives of MPB-07 employing the Zincke reaction for the construction of aromatic, quaternary ammonium salts such as those found in 2 or 3. In this transformation, primary amines react with highly electrophilic N-2,4-dinitrophenylpyridinium (DNP) salt 4 to afford pyridinium salt 8 with release of 2,4-dinitroaniline 6. Thus, the reaction of 1-(2,4-dinitrophenyl)pyridinium salts with various polymer-bound amino ethers, followed by cleavage from the resin, delivers the desired salts in good yield and high purity. 相似文献