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排序方式: 共有388条查询结果,搜索用时 31 毫秒
91.
Stuart Clough John Gupton Adepeju Ligali Matthew Roberts David Driscoll Scott Annett Alisa Hewitt Matthew Hudson Edward Jackson Robert Miller Bradley Norwood Rene Kanters Hadley Wyre Heather Petruzzi 《Tetrahedron》2005,61(31):7554-7561
The highly stereoselective conversions of (Z)-3-aryl-3-chloropropenals to (E)-3-alkoxy-3-arylpropenals, to (E)-3-aryl-3-morphorlinopropenals, and to vinamidinium salts are reported. The stereochemical assignments were based on 2D-NMR experiments. 相似文献
92.
A series of halotricarbonylmanganese chelate complexes, fac-(CO)3Mn(X)L (X = Cl (a), Br (b), I (c)), with thioformamide (L = Ph2PC(S)NRMe; R = H (1), Me (2), Ph (3)) and the isomeric thioformimidoester (L = Ph2PC(NR)SMe; R = Me (4), Ph (5)) ligands were prepared by thermal CO substitution of the pentacarbonylmanganese halides. The IR and NMR data indicate P,S-coordination of the ambidentate ligands and uniform Z configuration in 3–5. Due to the large linewidth of the NMR signals, the 4J(PH) and 3J(PC) coupling constants could not be determined for the thioamide complexes 1–3. Coordination of the thioimide 4 causes an increase in 4J(PH) whereas 3J(PC) remains unchanged. δ(31P) shows a downfield coordination shift as usual for manganese complexes. The broad 55Mn NMR signals cover a range of +90 to ?730 ppm (rel. KMnO4) with the imidoester complexes 4 and 5 at the low-field side. The normal halogen dependence Cl < Br < I is observed for 55Mn shielding. 相似文献
93.
Klaus Burger Lothar Hennig Annett Fuchs Dieter Greif Jan Spengler Fernando Albericio 《Monatshefte für Chemie / Chemical Monthly》2005,136(10):1763-1779
Summary. A new approach to trifluoromethyl substituted butenolides and their thioanalogues is described starting from 2-fluoro-3-trifluoromethylfurans
and -thiophenes, respectively. The reaction sequence includes three steps – nucleophilic displacement reaction, Claisen, and finally Cope rearrangement – which can be run as domino reaction. A modification of the domino reaction (transesterification instead of
Cope rearrangement) provides a concise access to α-trifluoromethyl-γ-ketoacids. 相似文献
94.
Kunze C 《Physical review. B, Condensed matter》1993,48(19):14338-14346
95.
Density gradient electrophoresis permits the separation of cell types according to surface charge density with high resolution. Any source of flow compromises the resolving power of density gradient electrophoresis. Although procedures have been devised to successfully counteract electroosmotic and convective flows, the final collection of separands requires that they be pumped out of the electrophoresis column. Experiments were therefore designed to test the hypothesis that this flow could also be eliminated by trapping the separated bands in a gel, from which they could be collected by slicing the gel cylinder. Glutaraldehyde-fixed rat and rabbit erythrocytes were used as test particles in a phosphate-buffered isotonic Ficoll-sucrose density gradient in a 2.2 cm diameter, thermostated vertical glass column that could be opened at both ends. Two types of agarose were used as gel polymers: Electrophoresis grade agarose (J.T. Baker Chemical Co.) at final concentrations of 0.1 to 0.25% and SeaPrep ultralow gelling agarose (Marine Colloids Div., FMC Corp.) at a final concentration of 1.0%. Electrophoretic separability of the test particles and fluid stability were tested independently at 55 degrees C and 32 degrees C at which the two agaroses were, respectively, liquid. The experiments demonstrated that the higher temperatures required and the presence of agarose compromised neither the stability of the density gradient nor the migration properties of the cells, and cells can be separated in a sol at a temperature that is compatible with cell viability. 相似文献
96.
97.
As strong nucleophiles, phosphorus ylids easily attack heteroallenes. The addition of isopropylidene triphenylphosphorane to carbon disulfide yields the zwitterionic adduct Ph3PCMe2CS2?, which reacts to bis(isopropylidene)-1,2,4-trithiolane by thermal or, coordinated to transition metals, photochemical activation according to a cycloaddition mechanism. By reaction of the betaine with manganese and rhenium carbonyl halides under exclusion of light, stable monomeric and dimeric fac-tricarbonyl complexes with the composition (CO)3M?(X)S2CCMe2PPh3 (M = Mn, Re; X = Cl, Br) are obtained which are distinguished by their spectra (IR, NMR, UV). The monomeric bromomanganese and -rhenium complexes are isomorphous and crystallize in the space group P2frcase1/c (monoclinic, Z = 4). 相似文献
98.
99.
[chemical reaction: see text]. The catalytic asymmetric Claisen rearrangement (CAC) of a highly substituted and functionalized alpha-alkoxycarbonyl-substituted allyl vinyl ether has been exploited to gain access to an advanced building block for the projected total synthesis of (-)-xeniolide F, the enantiomer of a xenicane diterpene isolated from a coral of the genus Xenia. 相似文献
100.
H. Procter Smith H. Rubricius H. Kunze H. Wdowiszewski W. Heike und J. J. Boyle 《Fresenius' Journal of Analytical Chemistry》1913,52(3-4):223-226
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