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81.
V. D. Sheludyakov Z. V. Belyakova V. M. Shevchenko E. A. Chernyshev 《Russian Chemical Bulletin》1997,46(5):997-1002
Novel dialkylaminocarbenium salts with metallocomplex counter ions were prepared by the reaction of phosgene with either DMF
or tetramethylurea in the presence of metal chlorides. Reactions of organosilicon amides with phosgene gave corresponding
carbenium salts, while organosilicon ureas yielded aminoiminocarbenium salts. Dialkylaminochlorocarbenium salts were reduced
with hydrosilanes to give dialkylaminocarbenium, salts and can be easily hydrolyzed to afford either amides or ureas. Pathways
of the reaction with water and alcohols depend on the nature of reagent and the reaction conditions.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1035–1040, May 1997. 相似文献
82.
The equilibrium constants, K
2, have been determined for the proton-transfer reactions of 1-phenacylquinolinium ion, PHQ+, with several amines {triethylamine (TEA), N,N,N′,N′-tetramethylethylenediamine (ED), N,N,N′, N′-tetramethylpropanediamine (PD), N,N,N′,N′-tetramethylbutanediamine (BD), and 1,8-bis(dimethylamino-naphthalene (DMAN)} in acetonitrile (AN), AN-tetrahydrofuran (THF)
and AN-ethanol (EtOH) mixtures. The reaction was followed spectrophotometrically using a stopped-flow technique. The K
2 value decreased for DMAN and increased for TEA with increasing vol-% of THF in AN-THF mixtures. The changes in the K
2 value for ED, PD and BD changed in the order: ED, PD and BD from a pattern similar to TEA to a pattern similar to DMAN. The
change in the K
2 value for DMAN with increasing vol-% of THF in AN-THF mixtures was explained by the effect of polarity on the stability of
P−Q+ (the deprotonated product of PHQ+). The effect of THF on the K
2 value is consistent with that of the peak wavelength of the absorption spectrum of P−Q+. The change in the K
2 value for TEA, ED, PD and BD depended on the structures of the protonated bases, one of the products for this reaction. The
effect of EtOH on the K
2 value for DMAN was examined in ternary EtOH-THF-AN mixtures that contain different amounts of EtOH and whose relative permittivities
were adjusted to that of EtOH. The K
2 value increased with increasing vol-% of EtOH because of the stabilization of P−Q+ upon the formation of the hydrogen-bonded complex with EtOH. The absorption spectrum of P−Q+ demonstrated a blue shift as the vol-% of EtOH increased. 相似文献
83.
β-Trifluoroacetyl vinyl ethers ROCHCHCOCF3 react smoothly as dienophiles with α,β-unsaturated carbonyl compounds to give the unexpected 2-alkoxyl-5-trifluoroacetyl-3,4-dihydro-2H pyrans. These products are formed by elimination and addition of the alcohol to the products of the normal hetero Diels-Alder reaction (2-alkoxyl-3-trifluoroacetyl-2,3-dihydro-2H pyrans). In contrast, 1,3-dipolar cycloaddition of ROCHCHCOCF3 with ArCHN(O)Me proceeds via a Z-endo transition state to give regio- and stereospecific 4-trifluoroacetyl substituted isoxazolidines and their derivatives. 相似文献
84.
Easily accessible N-acyl-2-triphenylphosphonioglycinate tetrafluoroborates react smoothly with trimethylphosphite in the presence of methyltriphenylphosphonium iodide to give N-acyl-2-(dimethoxyphosphoryl)glycinates in good or very good yields. The dimethoxyphosphorylglycinates may be isolated by column chromatography, or used directly for the Wadsworth-Emmons synthesis of α,β-dehydro-α-amino acids in a one-pot procedure without purification. 相似文献
85.
Cédric Kalinski Michael Umkehrer Nadine Jäger Wolfgang Hiller 《Tetrahedron letters》2006,47(12):2041-2044
A combinatorial synthetic route yielding fused tetrazolo[1,5-a]quinoxalines is described. The use of 2-fluorophenylisocyanide in the Ugi-tetrazole reaction (tetrazole-U-4CR) followed by a nucleophilic aromatic substitution (SNAr) affords the tricylic tetrazolo[1,5-a]quinoxaline moiety in good yields and with high diversity. 相似文献
86.
硫酸颜色反应用于荧光法测定利血平研究 总被引:6,自引:1,他引:6
提出了硫酸颜色反应用于利血平的荧光分析新方法。利用血平与浓硫酸反应,生成强荧光物质,所得产物的荧光强度与利血平的浓度在0-0.6μg/mL范围内有良好的线性关系。检测限为0.2ng/mL。本法可直接用于尿液中利血平的定量分析,回收率为82.5%-84.2%。 相似文献
87.
A new technique of searching the conformational space of transition states was used to explore the cause of the rate acceleration in the gem-dialkyl effect in intramolecular cyclization reactions. Several previous hypotheses were discarded and a new hypothesis was advanced based on this new data. This hypothesis, the “Facilitated Transition” hypothesis, states that increased steric hindrance reduces the overall activation energy by facilitating rotation through the transition state. The older “Reactive Rotamer” hypothesis was eliminated by generating all conformations of the starting materials using the
and
computer programs and demonstrating that no relationship is found between rate increase and a change in the concentration of “reactive rotamers”. 相似文献
88.
E. T. Denisov 《Russian Chemical Bulletin》2004,53(8):1602-1608
The transition state of addition of free radicals and atoms to multiple bonds is considered as a result of intersecting of two parabolic potential curves. One of them characterizes the stretching vibration of the attacked multiple bond, and another curve characterizes the stretching vibration of the bond formed in the transition state. The force constant of the latter is calculated by an empirical equation that correlates the force constant with the bond dissociation energy. In the framework of this model, the thermally neutral activation energy (E
e0) and the elongation of the attacked and formed bonds (r
e) in the transition state were calculated from the experimental data (activation energy (E
e) and enthalpy of reaction (H
e)) for the addition of an H atom and methyl, alkoxyl, aminyl, triethylsilyl, and peroxyl radicals to the C=C bond and the addition of H and CH3 to the C=O and CC bonds. Analysis of the data obtained showed that E
e0 depends linearly on the |H
e| + Ee sum, i.e., Ee0/kJ mol–1 = 14.2 + 0.61 · (Ee – H
e), and the bond elongation in the transition state for addition of the most part of radicals to ethylene and acetylene vary within (0.65–0.87)·10–10 m. The factors affecting the activation energy of the radical addition reactions are discussed.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1542–August, 2004. 相似文献
89.
V. Z. Shirinian M. M. Krayushkin D. M. Nikalin A. A. Shimkin 《Russian Chemical Bulletin》2005,54(3):738-742
The reaction of alkyl 4-(2-acetylhydrazino)-2-methyl-3-thiophenecarboxylates with 3-methylbutan-2-one was carried out under the Fischer reaction conditions. The influence of Lewis acids and solvents on the process was studied. A convenient method for the synthesis of thieno [3.2-b]pyrrolenine derivatives was proposed.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 725–729, March, 2005. 相似文献
90.
Method for the synthesis of m-and p-isomers of 4-[2-(ethynylphenyl)vinyl]-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxides by the cross-coupling of 4-[2-(3-iodophenyl)vinyl]-and
4-[2-(4-iodophenyl)vinyl]-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxides with (trimethylsilyl)acetylene followed by desilylation
was elaborated. The reactions at the CH-fragment of the ethynyl group were performed. The Mannich reaction proceeds with the
loss of a spin label, whereas the oxidative homocoupling, with its retention.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2051–2054, October, 2007. 相似文献