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71.
A new synthetic method is described for the mild and selective reduction of 3-methyl-5-aryl-1,2,4-oxadiazoles to amidines employing iron powder in aqueous medium. Its application is demonstrated in the synthesis of 1, a potent and selective urokinase-type plasminogen activator (uPA) inhibitor. 相似文献
72.
Chlorided 0.57 wt. % Pt/γ-Al2O3 is a moderately active and highly selective catalyst for the isomerization of n-hexane at 300 °C when an excess of H2 is present. Chlorine, which is continuously lost from the catalyst, may be replaced by adding a small amount of chloroform to the reactant stream. The catalyst exhibits activity and high isomerization selectivity even at 150 °C. Under the conditions of these lower temperature experiments, the equilibrium concentration of C6 alkenes would be only 8 × 10?7 Torr. This suggests that the classical mechanism, which involves the formation of n-hexene on the Pt, is not applicable. Rather, it is proposed that isomerization of the alkane occurs at acid sites on the catalyst, and the role of Pt is to catalyze the hydrogenation of any alkenes that might be formed as a result of cracking reactions. At temperatures ≤ 300 °C Brönsted acid sites are present in the catalyst, and presumably are responsible for the isomerization and cracking activity, but at higher temperatures Lewis acid sites play a dominant role. 相似文献
73.
David N.-S. Hon Josefina M. San Luis 《Journal of polymer science. Part A, Polymer chemistry》1989,27(12):4143-4160
Cyanoethylation was attempted to convert wood into thermoplastic material as a means to utilize low quality wood species as well as wood waste materials. Cyanoethylation reaction was conducted with control of the alkalinity of the reaction media, reaction temperature and time, and wood-to-acrylonitrile ratio. Cyanoethylated wood was purified and its nitrogen content and weight gain were determined. Fourier transform infrared (FTIR) spectroscopy was used to monitor the absorption peak of cyano group. Thermoproperties of cyanoethylated wood were analyzed by means of a differential scanning calorimeter (DSC) and a dynamic mechanical thermal analyzer (DMTA). Reaction mechanisms and chemistry influencing the thermoproperties of cyanoethylated wood were discussed. 相似文献
74.
Souza J Molfetta FA Honório KM Santos RH da Silva AB 《Journal of chemical information and computer sciences》2004,44(3):1153-1161
The AM1 semiempirical method is employed to calculate a set of molecular properties (variables) of 45 flavone compounds with antipicornavirus activity, and 9 new flavone molecules are used for an activity prediction study. Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), Stepwise Discriminant Analysis (SDA), and K-Nearest Neighbor (KNN) are employed in order to reduce dimensionality and investigate which subset of variables should be more effective for classifying the flavone compounds according to their degree of antipicornavirus activity. The PCA, HCA, SDA, and KNN methods showed that the variables MR (molar refractivity), B(9) (bond order between C(9) and C(10) atoms), and B(25) (bond order between C(11) and R(7) atoms) are important properties for the separation between active and inactive flavone compounds, and this fact reveals that electronic and steric effects are relevant when one is trying to understand the interaction between flavone compounds with antipicornavirus activity and the biological receptor. In the activity prediction study, using the PCA, HCA, SDA, and KNN methodologies, three of the 9 new flavone compounds studied were classified as potentially active against picornaviruses. 相似文献
75.
Kun-Chun Hsieh Chun-Liang Lai Hon Man Lee Shie-Ming Peng 《Journal of organometallic chemistry》2004,689(21):3362-3369
A bis(diethylamido)hafnium compound [C4H3N(CH2NMe2)-2]2Hf(NEt2)2 (1) has been prepared in 79% yield by reacting Hf(NEt2)4 with 2 equiv. of [C4H3NH(CH2NMe2)-2] in heptane via deamination. Reacting compound 1 with 2 equiv. of phenyl isocyanate at room temperature in diethyl ether results in the PhNCO being inserted seletively into hafnium-NEt2 bonds to generate [C4H3N(CH2NMe2)-2]2Hf[PhNC(NEt2)O]2 (2) in 56% yield. Similarly, while reacting 1 with 2 equiv. of phenyl isocyanate for a week in toluene produces a mixture of 2 and [C4H3N(CH2NMe2)-2]Hf[PhNC(NEt2)O]3 (3). For comparison, reacting Hf(NEt2)4 with 4 equiv. of PhNCO in a toluene solution at room temperature results in the PhNCO inserted into Hf-N bonds, and forms a tetrakis-ureato hafnium compound Hf[PhNC(NEt2)O]4 (4) in 88% yield. A theoretical calculation found that the unpaired electrons of the ureato fragments of 2 are resonance delocalized between the C-O, C-NPh, and C-NEt2 bonds, which are all partially doubly bonded. 相似文献
76.
Yung-Son Hon Tzyy-Rong HsuChun-Yan Chen Yi-Hui LinFong-Jong Chang Cheng-Han HsiehPing-Hui Szu 《Tetrahedron》2003,59(9):1509-1520
The reactivity of aryl alkyl ketone with a preheated mixture of dibromomethane and diethylamine is poor and gives an α-methylenation product in very low yield even under refluxing condition. It can be accelerated dramatically by microwave irradiation. Under microwave condition, the cyclic 1,3-dicarbonyls, aryl alkyl ketones, heteroaryl alkyl ketones and acyclic benzyl ketone give α-methylenation products in modest to good yields. 相似文献
77.
Alan R. Burns Ama?l G. E. Madec Darryl W. Low Iain D. Roy Hon Wai Lam 《Chemical science》2015,6(6):3550-3555
2,2-Disubstituted cyclic 1,3-diketones containing a tethered electron-deficient alkene undergo chiral phosphoric acid-catalyzed desymmetrizing Michael cyclizations to give bridged bicyclic products in high enantioselectivities. Both bicyclo[3.2.1]octanes and bicyclo[3.3.1]nonanes are accessible using this methodology. 相似文献
78.
N.-S. Hon 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):1175-1192
The objective of this work was to study the effect of solar radiation on cellulose by means of ESR techniques. It is shown by ESR spectra that outdoor exposure of cellulose to concentrated sunlight, regardless of the presence of oxygen and sensitizer, causes the polymer to degrade via free-radical processes. Particularly, it is shown that main-chain scission occurs under solar radiation. This phenomenon is accompanied by the formation of peroxide when oxygen is present. It is also revealed that photooxidation leads ultimately to discoloration of the polymer at exposed surfaces. 相似文献
79.
Radiation-induced wood-polymer composites have been prepared using some tropical commercial woods. These included Kapur (Dryobalanop sp.), Kempas (Koompassia sp.), Red Seraya (Shorea sp.), White Seraya (Parashorea sp.), and Jelutong (Dyera sp.). The wood specimens were modified by impregnation with monomers and followed by exposure to gamma radiation. Monomer systems used were methyl methacrylate, methyl methacrylate with 5% dioxane, acrylonitrile, 60:40 styrene-acrylonitrile comonomer, vinyl acetate, and vinylidene chloride. The resulting composite specimens exhibited significant increases in hardness and compressive strength, the extent of which appeared to depend on the amount and type of polymer present. Dimensional stability increased when the woods were impregnated with polymethyl methacrylate and improved further to about 35% on addition of a swelling agent, dioxane. Wood-polyvinylidene chloride composites gave high fire resistance as opposed to wood-polymethyl methacrylate which showed increased flammability. A 4-fold decrease in weight loss was observed in the fire-tube and crib tests conducted. The impregnated polymers were not totally resistant to termites. The polymers, not being nutrients, reduced the number of survivals after a 90-d test period. Polystyrene-acrylonitrile appeared toxic to the termites. 相似文献
80.
The purpose of this study was to analyze background parenchymal enhancement (BPE) in the contralateral normal breast of cancer patients during the course of neoadjuvant chemotherapy (NAC). 相似文献