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941.
Synthesis and structure of 2,5,7,10-tetramethyl-2,4,8,10-tetraazabicyclo[4.4.0]decane-3,9-dione 总被引:1,自引:0,他引:1
M. O. Dekaprilevich A. N. Kravchenko L. I. Khmel'nitskii O. V. Lebedev Yu. T. Struchkov Yu. A. Strelenko 《Russian Chemical Bulletin》1995,44(1):131-133
2,5,7,10-Tetramethyl-2,4,8,10-tetraazabicyclo[4.4.0]decane-3,9-dione, a regioisomer of the previously known 2,5,7,8-tetramethyl-2,4,8,10-tetraazabicyclo[4.4.0]decane-3,9-dione, has been synthesized, and its structure has been established by X-ray diffraction analysis. The bicyclic system of this molecule is formed by two heterocyclescis-annelated through the C(1)-C(6) bond. The relative configurations of the asymmetric centers areS for C(5), andR for C(7). In the monohydrate crystal studied, the molecules are linked by O...H-Ow and O...H-N type H-bonds forming a three-dimensional framework.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 136–138, January, 1995. 相似文献
942.
943.
Heterogeneous palladium catalysts anchored on functionalized silica were prepared by sol–gel methods and their catalytic properties for the oxidative carbonylation of phenol to diphenyl carbonate (DPC) were investigated. The catalysts were characterized by means of IR, XPS, EA and BET. The Pd loading in the heterogeneous catalysts and leaching in solution were detected by atomic absorption. The effects of different reaction parameters such as temperature, solvent and inorganic cocatalyst on the yield of DPC and Pd leaching were also studied. It was found that Cu2O and tetrahydrofuran (THF) were the best partners with these heterogeneous catalysts. In the presence of 3 Å molecular sieves as dehydrating agent, the heterogeneous palladium catalyst prepared from 2‐acylpyridine revealed excellent catalytic performance and stability at 110 °C for 5 h, giving 13.7% yield of DPC based on phenol and 4.0% Pd loss in solution. The heterogeneous catalyst was more active and stable compared with traditional supported Pd? C catalyst under the same reaction conditions. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
944.
Alexey P. Ilyin Julia N. Peregudova Elena B. Poutsykina Dmitri V. Kravchenko 《Tetrahedron letters》2006,47(15):2649-2653
We present a convenient synthesis of heterocyclic scaffolds using a novel modification of four-component Ugi condensation. Two complementary variants of this useful synthetic strategy provide an efficient one-step assembly of four novel pharmaceutically relevant (hetero)aryl-fused 1,4-oxazepines with different substituents’ profile. 相似文献
945.
《Angewandte Chemie (International ed. in English)》2017,56(33):9990-9993
The thermal reduction of N2O by CO mediated by the metal‐free cluster cations [Si2Ox].+ (x =2–5) has been examined in the gas phase using Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometry in conjunction with quantum chemical calculations. Three successive oxidation/reduction steps occur starting from [Si2O2].+ and N2O to form eventually [Si2O5].+; the latter as well as the intermediate oxide cluster ions react sequentially with CO molecules to regenerate [Si2O2].+. Thus, full catalytic cycles occur at ambient conditions in the gas phase. Mechanistic aspects of these sequential redox processes have been addressed to reveal the electronic origins of these unparalleled reactions. 相似文献
946.
《化学:亚洲杂志》2017,12(18):2426-2433
Exploring non‐precious‐metal‐based oxygen reduction reaction (ORR) electrocatalysts featuring high efficiency, low cost, and environmental friendliness is of great importance for the broad applications of fuel cells and metal–air batteries. In this work, ultrathin NiCo2O4 nanosheets deposited on 1D SnO2 nanotubes (SNT) were successfully fabricated through a productive electrospinning technique followed by a sintering and low‐temperature coprecipitation strategy. This hierarchically engineered architecture has ultrathin NiCo2O4 nanosheets uniformly and fully erected on both walls of tubular SNTs, which results in improved electrochemical activity as an ORR catalyst, in terms of positive onset potential and high current density, as well as superior tolerance to crossover effects and long‐term durability with respect to the commercial Pt/C catalyst. The excellent performance of SNT@NiCo2O4 composites may originate from their rationally designed hierarchical tubular nanostructure with completely exposed active sites and interconnected 1D networks for efficient electron and electrolyte transfer; this makes these composite nanotubes promising candidates to replace platinum‐based catalysts for practical fuel cell and metal–air battery applications. 相似文献
947.
Space transportation systems require high-performance thermal protection and fluid management for systems ranging from cryogenic fluid devices to primary structures, and for propulsion systems exposed to extremely high temperatures, and other space systems, e.g., integrated circuits and cooling/environment control devices for advanced space suits. Although considerable developmental effort is underway to bring promising technologies to a readiness level for practical use, new and innovative methods are still needed. One such method is the Advanced Micro Cooling Module (AMCM), essentially a compact two-phase heat exchanger constructed of microchannels and designed to rapidly remove large quantities of heat from critical systems by incorporating phase transition. This paper describes the results of experimental research in two-phase flow phenomena, encompassing both an experimental and an analytical approach to the incorporation of flow patterns for air–water mixtures flowing in microchannels. Specifically addressed are: (1) design and construction of a sensitive two-phase experimental system which measures both ac and dc components of in situ physical mixture parameters including spatial concentration, using concomitant methods; (2) data acquisition and analysis in the amplitude, time, and frequency domains; and (3) analysis of results including evaluation of in situ physical parameters, and assessment of their validity for application in flow pattern determination. 相似文献
948.
Stereoselective construction of the tricyclic core of yonarolide (1), a marine norditerpenoid, was achieved. This synthetic route includes a Diels-Alder reaction and an intramolecular aldol condensation. It also involves efficient epimerization through a retro-Michael reaction-Michael addition and will be applicable to the total synthesis of 1. 相似文献
949.
A new chemical access has been developed for the synthesis of 3′-acetyl-4′-hydroxychalcones from 1-(5-acetyl-2-hydroxy-phenyl)-ethanone and various substituted benzaldehydes via a regioselective Claisen-Schmidt condensation using borontrifluoride-etherate (BF3·OEt2) at room temperature, in good to excellent yields within 12-24 h. Application of this methodology has also been demonstrated in the synthesis of chalcone hybrids. 相似文献
950.