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121.
Data characterizing the position of the equilibrium between Δ2- and Δ1-pyrazolines with alkyl substituents in different positions, which is established under the influence of potassium tertbutoxide in tert-butyl alcohol at 90°C, were obtained. 3-Alkyl-Δ2-pyrazolines are thermodynamically more stable than their isomers with different positions of the double bond, so that the fraction of the latter in equilibrium mixtures does not exceed 1–2%, and they are practically completely isomerized to the 3-Alkyl-Δ2-substituted derivatives. If the position of the side chains excludes the possibility of the formation of 3-alkyl-Δ2-pyrazolines by migration of the double bond (4-alkyl- and 5,5-dialkyl-substituted compounds), the fraction of Δ1-pyrazolines in the equilibrium rises appreciably and reaches 12% for 3,3-diethyl-Δ1-pyrazoline. 相似文献
122.
Roman A. Kunetsky Marina I. Struchkova Vladimir A. Tartakovsky Sema L. Ioffe 《Tetrahedron letters》2005,46(31):5203-5205
An approach to conjugated nitroalkenes via oxidation of N,N-bis(silyloxy)enamines with bromine or iodine in the presence of tetra-n-butylammonium acetate is described. The acetate ion plays a key role by acting as a mild desilylating reagent. This new strategy allows the synthesis of α-nitroalkenes from the corresponding nitroalkanes. 相似文献
123.
Ioffe V Kalendarev T Rubinstein I Zabetski R Zupkovitz G 《Journal of chromatography. A》2004,1031(1-2):249-258
Phospholipid derivatives of methotrexate (MTX) having enhanced membrane penetration (DP-71 being the most important) are potential prodrugs for treatment of autoimmune and inflammatory diseases as well as diseases involving abnormal cell proliferation. The previously published reversed-phase HPLC methods for similar compounds, phospholipid derivatives of valproic acid and non-steroidal anti-inflammatory drugs (NSAIDs), could not be used for MTX derivatives due to highly basic character of the MTX core molecule. The new HPLC procedure using gradient elution was developed as a compromise between the pharmacopoeial method for MTX and the previous "generic" procedure for phospholipid derivatives of NSAIDs. The newly developed method is sensitive, selective, reproducible, and stability indicating. Identification of major related compounds was carried out. The bioanalytical applications of this method, as well as of the derived isocratic procedure, are discussed and illustrated by examples of pharmacokinetic studies. 相似文献
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A. D. Ioffe 《Proceedings of the American Mathematical Society》2008,136(9):3111-3119
We prove three theorems extending Sard's theorem and its infinite dimensional extension due to Smale to set-valued mappings with stratifiable graphs. The very concept of a critical value comes from (nonsmooth) variational analysis and turns out to be perfectly compatible with the natural condition defining ``good' stratifications (e.g., Whitney stratification in the finite dimensional case).
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Orienting Effect of the Cage Addends: The Case of Nucleophilic Cyclopropanation of C2‐C70(CF3)8
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Dr. Marina G. Apenova Olesya O. Semivrazhskaya Eugenia V. Borkovskaya Nikita M. Belov Dr. Ilya N. Ioffe Dr. Vitaliy Yu. Markov Prof. Dr. Sergey I. Troyanov Dr. Natalia S. Lukonina Prof. Dr. Lev N. Sidorov Dr. Alexey A. Goryunkov 《化学:亚洲杂志》2015,10(6):1370-1378
C2‐C70(CF3)8 was found to be a very promising substrate in the Bingel and the Bingel–Hirsch reactions combining perfect regioselectivity with much higher reactivity compared to its analogs. The reactions with diethyl malonate yield a single isomer of the monoadduct C70(CF3)8[C(CO2Et)2] and a single C2‐symmetrical bisadduct C70(CF3)8[C(CO2Et)2]2. The Bingel–Hirsch variation is particularly interesting in that it additionally affords, in a similar regioselective manner, the unexpected alkylated derivatives C70(CF3)8[CH(CO2Et)2]H and C70(CF3)8[C(CO2Et)2][CH(CO2Et)2]H. The novel compounds have been isolated and structurally characterized by means of 1H and 19F NMR spectroscopy as well as single‐crystal X‐ray diffraction. The mechanistic and regiochemical aspects of the reaction are explained with the aid of DFT calculations. 相似文献
130.
We develop a semi-quantitative theory of electron pairing and resulting superconductivity in bulk “poor conductors” in which Fermi energy EF is located in the region of localized states not so far from the Anderson mobility edge Ec. We assume attractive interaction between electrons near the Fermi surface. We review the existing theories and experimental data and argue that a large class of disordered films is described by this model.Our theoretical analysis is based on analytical treatment of pairing correlations, described in the basis of the exact single-particle eigenstates of the 3D Anderson model, which we combine with numerical data on eigenfunction correlations. Fractal nature of critical wavefunction's correlations is shown to be crucial for the physics of these systems.We identify three distinct phases: ‘critical’ superconductive state formed at EF = Ec, superconducting state with a strong pseudo-gap, realized due to pairing of weakly localized electrons and insulating state realized at EF still deeper inside a localized band. The ‘critical’ superconducting phase is characterized by the enhancement of the transition temperature with respect to BCS result, by the inhomogeneous spatial distribution of superconductive order parameter and local density of states. The major new feature of the pseudo-gapped state is the presence of two independent energy scales: superconducting gap Δ, that is due to many-body correlations and a new “pseudo-gap” energy scale ΔP which characterizes typical binding energy of localized electron pairs and leads to the insulating behavior of the resistivity as a function of temperature above superconductive Tc. Two gap nature of the pseudo-gapped superconductor is shown to lead to specific features seen in scanning tunneling spectroscopy and point-contact Andreev spectroscopy. We predict that pseudo-gapped superconducting state demonstrates anomalous behavior of the optical spectral weight. The insulating state is realized due to the presence of local pairing gap but without superconducting correlations; it is characterized by a hard insulating gap in the density of single electrons and by purely activated low-temperature resistivity ln R(T) ∼ 1/T.Based on these results we propose a new “pseudo-spin” scenario of superconductor-insulator transition and argue that it is realized in a particular class of disordered superconducting films. We conclude by the discussion of the experimental predictions of the theory and the theoretical issues that remain unsolved. 相似文献