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71.
Rhodium(II)-catalyzed reactions of cyclic diazodicarbonyl compounds with a variety of halides have been examined. With acid halides, β-acyloxy α-haloenones are produced in good yields. With benzyl halides, β-benzyloxy α-haloenones are obtained in good yields. Reactions with methylene halides yield β-halomethoxy α-haloenones in good yields, whereas reactions with ethyl halides and ethylene dihalides result in β-hydroxy α-haloenones in high yields. These reactions provide a useful and rapid entry to β-substituted α-haloenones. The mechanistic pathway for the formation of these products has been also described in terms of halonium ylides. 相似文献
72.
A palladium-catalyzed asymmetric allylic alkylation effects a dynamic kinetic asymmetric transformation of racemic isoprene monoepoxide and a surrogate for Nazarov's reagent in which a quaternary center is created with exellent ee. The resultant adduct allows easy access to a substrate for ring-closing metathesis to form a cyclopentenone and sets the stage for an 11-step synthesis of the cyclopentyl core of the antibiotic antitumor agent viridenomycin. [reaction: see text] 相似文献
73.
[Chemical reaction: See text] We have developed a general, efficient, and inexpensive catalyst system for arylation of amines by using 10 mol % of CuI as the copper source, 20 mol % of diphenyl pyrrolidine-2-phosphonate (DPP) as the ligand, K3PO4 as the base, and DMF containing 2% water (v/v) as the solvent. 相似文献
74.
Xu X Zhao J Jiang D Kong J Liu B Deng J 《Analytical and bioanalytical chemistry》2002,374(7-8):1261-1266
A novel hydrogen peroxide biosensor was developed based on the immobilization of horseradish peroxidase (HRP) in a TiO(2) sol-gel matrix on an electropolymerized phenazine methosulfate (PMS) modified electrode surface. Such membranes are of interest due to their high surface area, biological compatibility, and ease of fabrication. HRP entrapped in the TiO(2) matix was stable and retained its activity to a large extent. Cyclic voltammetry and amperometric measurements were employed to demonstrate the feasibility of electron transfer between immobilized HRP and the glassy carbon electrode via electropolymerized PMS. The influence of various experimental parameters such as operating potential, pH, temperature, and stability was investigated for optimum analytical performance. The biosensor provided a wide linear calibration range from 4.0x10(-6) M to 1.0x10(-3) M, with a detection limit of 8.0x10(-7) M at a signal-to-noise ratio of 3. The sensor retained 80% of its original activity after two months of operation. 相似文献
75.
Thenp P Rydberg sequence of neutral Ytterbium is strongly perturbed. These perturbations were monitored by measuring theg J factors and lifetimes of 19 states, including both singlets and triplets as well as states from the perturbing configurations. A pulsed laser setup was used. Theg J factors were obtained from a Zeeman quantum-beat experiment and the lifetimes by direct observation of the decay of the fluorescence light. 相似文献
76.
Ying-nan Xuan Yan Gao Yong Huang Xi-gao Jian Laboratory of Cellulose Lignocellulosics Chemistry Guangzhou Institute of Chemistry Chinese Academy of Sciences Guangzhou China Institute of Chemistry Chinese Academy of Sciences Beijing China Department of Polymer Science College of Chemical Engineering Dalian University of Technology Dalian China 《高分子科学》2002,(3):225-229
A kind of novel heat-resistant, high performance engineering thermoplastic phthalazinone poly(aryl ether sulfoneketone) (PPESK) containing a carboxyl group in its side chain was prepared by the nucleophilic displacement reaction of 4-(4-hydroxylphenyl)-1(2H)-phthalazinone with di(4-chlorophenyl) sulfone, 4,4'-difluoro-benzophenone and phenolphthalin insulfolane in the presence of K_2CO_3 to produce high molecular weight polymers which can be dissolved in some polarsolvents such as chloroform and nitrobenzene at room temperature and can be easily can into flexible, yellowish andtransparent films. PPESK is an amorphous polymer having a decomposition temperature above 400℃, which indicates that ithas high thermal stability. At the same time, the thermal properties of PPESKs with dicyandiamide (DICY) as curing agentindicated that the heat-resistance properties of the PPESKs are improved after curing. The apparent activation energy (ΔE) ofthe cross-linking reaction and the reaction order (n) of PPESK/DICY were found to be 52.2 kJ/mol and ca. 1.0, respectively.Therefore, the cross-linking reaction is approximately a first order reaction. 相似文献
77.
Some localized singlet 1,3-σ-diradicals, C(MH2)3C, (M = Si, Ge, Sn, Pb) were theoretically designed by the orbital phase theory and density functional theory calculations. The bicyclic carbon-centered singlet diradicals were more stable than the lowest triplets. Except for M = C, σ-bonded isomers were not located for 1,3-σ-diradicals. 1,4-σ-diradicals, C(M2H4)3C, also had singlet ground states, but they were less stable than σ-bonded isomers. 相似文献
78.
Ke Jian Liu Jin Jie Jiang Li Li Ji Xianglin Shi Harold M. Swartz 《Research on Chemical Intermediates》1996,22(5):499-509
Application of the spin trapping technique in intact animals requires an understanding of the stability and distribution of the spin traps and their spin adducts in vivo. We studied the stability of DMPO in vivo in mice using HPLC and the stability of spin adducts of DMPO by EPR in plasma, whole blood, peritoneal fluid, and homogenized heart tissue of the rat. At 15 minutes after intraperitoneal injection DMPO had similar concentrations in the liver, heart, and blood of the mice and 40% remained in the organs 2 hours after the injection. In contrast, the spin adduct DMPO-OH was short lived, with a half-life of 3.0 minutes in plasma, and was not detectable 1 minute after formation in whole blood and homogenized heart tissue. The carbon centered spin adduct DMPO-CH(OH)CH3 was more stable, having half-lives of 16, 11, 3.6, and 0.79 minutes in plasma, peritoneal fluid, whole blood, and homogenized heart tissue, respectively. The spin adduct DMPO-SO3 was sufficiently stable for the adduct to be observed directly from living mice. 相似文献
79.
用水热法合成了云母蒙脱石,并与羟基铝齐聚物交联,DTA和IR结果表明,由于柱的引进,高温焙烧时层内八面体上羟基脱除变得较为容易。由NH_3-TPD和吡啶吸附测得的表面酸性表明Al-CLS具有较SMM更多的弱酸和强酸中心。催化剂上弱酸中心有利于醇的脱水,而吸附在强酸中心上的NH_3有利于醇的胺化。 相似文献
80.
Can one join both ends of a helix? A helical aromatic oligoamide was macrocyclized into a saddle-shaped bifunctional clip molecule that self-assembles into discrete circular dodecamers in the solid state and shows great potential for binding aromatic acid guests in solution. The cyclization step requires that the helix is only partly denatured in the reaction medium. 相似文献