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41.
Inga Cikotiene Erika Pudziuvelyte Algirdas Brukstus 《Journal of heterocyclic chemistry》2008,45(6):1615-1620
A relatively short and efficient method for the utilization of 4,6‐dichloro‐2‐methylthio‐5‐nitropyrimidine ( 1 ) in the synthesis of the poly substituted pyrrolo[3,2‐d]pyrimidin‐7‐one 5‐oxides ( 6a ‐g) is reported. Some new 4‐substituted 6‐chloro‐2‐methylthio‐5‐nitropyrimidines ( 2a‐e ) were prepared by reaction of 4,6‐dichloro‐2‐methylthio‐5‐nitropyrimidine ( 1 ) with amines. 4‐Substituted 2‐methylthio‐5‐nitro‐6‐phenylethynylpyrimidines ( 3a‐e ), obtained from 4‐substituted 6‐chloro‐2‐methylthio‐5‐nitropyrimidines ( 2a‐e ) via palladium‐catalyzed Sonagashira coupling reaction with 1‐phenylacetylene, underwent smooth cyclization reaction in boiling 2‐propanol in the presence of catalytic amount of pyridine to give 4‐substituted 2‐methylthio‐6‐phenyl‐7H‐pyrrolo[3,2‐d]pyrimidin‐7‐one 5‐oxides ( 4a‐e ). The methylthio group of the latter compounds can be easily and selectively oxidized by m‐chloroperbenzoic acid and replaced with different amines. 相似文献
42.
The title cyclohexenone 1d undergoes photodimerization selectively at the exocyclic C?C bond to give a 1 : 1 mixture of 1,2‐dialkynyl‐1,2‐dimethylcyclobutanes 6 and 7 . On irradiation in the presence of 2,3‐dimethylbuta‐1,3‐diene, 1d affords bicyclo[8.4.0]tetradeca‐1,2,3,7‐tetraen‐11‐one 9 . This – formal – (6+4)‐cycloadduct undergoes quantitative isomerization to 3‐cycloheptadienyl‐2,5,5‐trimethylcyclohex‐2‐enone 11 on treatment with basic silica gel. 相似文献
43.
Inga M. Arkhipova Angelo Luongo 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2016,67(3):69
The effect of damping on the re-stabilization of statically unstable linear Hamiltonian systems, performed via parametric excitation, is studied. A general multi-degree-of-freedom mechanical system is considered, close to a divergence point, at which a mode is incipiently stable and n ? 1 modes are (marginally) stable. The asymptotic dynamics of system is studied via the Multiple Scale Method, which supplies amplitude modulation equations ruling the slow flow. Several resonances between the excitation and the natural frequencies, of direct 1:1, 1:2, 2:1, or sum and difference combination types, are studied. The algorithm calls for using integer or fractional asymptotic power expansions and performing nonstandard steps. It is found that a slight damping is able to increase the performances of the control system, but only far from resonance. Results relevant to a sample system are compared with numerical findings based on the Floquet theory. 相似文献
44.
Grigoraviciute I Yamauchi H Karppinen M 《Journal of the American Chemical Society》2007,129(9):2593-2596
Among high-Tc superconductive copper oxides, there have been known phases that contain fluorite-structured layers as an additional "blocking block" between adjacent CuO2 planes. Here, we report that even a phase with the CuO2 planes separated by a 12-A thick quadruple-fluorite-layer block can be synthesized in a single phase and strongly oxygenated form to exhibit superconductivity with a Tc value as high as 55 K. The new phase is the fourth member of the (Cu,Mo)Sr2(Ce,Y)sCu2O(5+2s+delta) or (Cu,Mo)-12s2 homologous series. Comparison with the previously known s = 1, 2, and 3 members of the series reveals the amazing conclusion that Tc remains essentially unaffected upon inserting additional fluorite-structured layers between the two CuO2 planes as long as the hole-doping level of the planes is kept constant. 相似文献
45.
About the Effect of Substitution on the Crystal Structure of SrNi2P2 With several series of mixed crystals the effect of substitution on the crystal structure of SrNi2P2 (polymorphic, the structures are variants of the ThCr2Si2 type) is investigated by X-ray methods. In the compound Ni completely can be substituted by Co and Cu respectively and also P by As; in Sr1–xCaxNi2P2 there is a gap of the miscibility between 0.3 ≤ x ≤ 0.6. A low substitution of the several elements more than proportionally changes the structure parameters. In this range the mixed crystals with Ca, Cu, and As, respectively, undergo first order phase transitions with significant changes of the bond distances, which will be interpreted by the results of band structure calculations. 相似文献
46.
Ca3Pd4Bi8: Crystal and Electronic Structure Ca3Pd4Bi8 (a = 10.814(4), b = 17.050(6), c = 4.149(4) Å) was prepared by heating the elements at 900 °C and investigated by single crystal X‐ray methods. The compound crystallizes in a new structure type (Pbam; Z = 2). Six Bi atoms form distorted trigonal prisms around the Pd atoms. The polyhedra share common corners, edges or faces building up a three dimensional Pd, Bi network, whose holes are occupied by Ca atoms. A special feature is a distorted octahedron of four Pd and two Bi atoms connected via short homonuclear bonds. The metallic behaviour of the compound derived from the bond lengths is discussed by LMTO band structure calculations. 相似文献
47.
Synthesis and Crystal Structure of A Cu4As2 ( A : Ca–Ba, Eu) Steel‐gray single crystals of ACu4As2 with A = Ca–Ba and Eu respectively were synthesized by heating mixtures of the elements at about 900 °C. Structure determinations with X‐ray diffractometry data revealed, that the isotypic compounds crystallize in the rhombohedral CaCu4P2 type structure (R3m; Z = 3) (hexagonal axes see ”︁Inhaltsübersicht”︁”︁). Measurements of the susceptibility of EuCu4As2 showed divalent Eu and ferromagnetic order at 35 K. 相似文献
48.
Janka M He W Haedicke IE Fronczek FR Frontier AJ Eisenberg R 《Journal of the American Chemical Society》2006,128(16):5312-5313
The first examples of a tandem Nazarov cyclization/Michael addition process are described. The sequence is efficiently catalyzed by Ir[Me(CO)(dppe)(DIB)]2+ and occurs with high diastereoselectivity, creating three contiguous stereocenters. The mechanistic factors controlling the reactivity and diastereoselectivity are discussed. 相似文献
49.
Bringmann G Kajahn I Reichert M Pedersen SE Faber JH Gulder T Brun R Christensen SB Ponte-Sucre A Moll H Heubl G Mudogo V 《The Journal of organic chemistry》2006,71(25):9348-9356
The isolation and structural elucidation of three novel-type naphthylisoquinoline alkaloids, ancistrocladinium A and B (the latter along with its atropisomer), from a Congolese Ancistrocladus species collected in the habitat Yeteto is reported. Their structures, including all stereochemical features, were elucidated by spectroscopic, chemical, and chiroptical methods. Ancistrocladinium A and B are the first N,C-coupled naphthyldihydroisoquinoline alkaloids found in nature, i.e., with an iminium-aryl axis. Although ancistrocladinium A, which is N,8'-coupled, is configurationally stable at this axis, ancistrocladinum B and its rotational isomer are based on a hitherto unprecedented N,6'-coupling type, with a slow rotation about the hetero biaryl axis at room temperature; they thus occur as a 46:54 mixture of two configurationally semistable atropo-diastereomers. For the isomerization of (P)-ancistrocladinium B to its (M)-diastereomer and for the opposite direction, the Gibbs free energies of activation were determined to be DeltaG double dagger1 = 105.8 kJ mol-1 and DeltaG double dagger2 = 105.7 kJ mol-1, respectively. In addition, the compounds were shown to have promising antileishmanial activities. 相似文献
50.
Andrius Garbaras Justina Šapolaitė Inga Garbarienė Žilvinas Ežerinskis Agnė Mašalaitė-Nalivaikė Raminta Skipitytė 《Isotopes in environmental and health studies》2018,54(5):463-474
In the present study, a combination of the stable carbon isotope ratio (13C/12C) with radiocarbon data (14C) allowed us to perform the aerosol source apportionment. Filter samples of PM1 were collected during the warm and cold periods in rural and urban sites in Lithuania. The 14C/12C ratio of total carbon (TC) was measured using the single stage accelerator mass spectrometer quantifying of fossil and non-fossil derived aerosol emissions. The δ13C value was measured using an elemental analyser interfaced with an isotope ratio mass spectrometer. We have found that the highest fraction of contemporary carbon (fc?=?0.82) was measured during a warm period in a rural location. A higher fraction of fossil fuel-derived carbon was observed for air masses transported from highly industrialized Western European regions during both seasons. Isotope mass balance calculations revealed that the traffic emissions composed 15 and 25?% in rural and urban sites, respectively, and did not change during either season. Input from coal-derived aerosol particles was estimated to be 15?% at an urban site during the cold period. The combination of the stable carbon isotope ratio with the radiocarbon data allowed us to distinguish coal, liquid fossil fuel combustion, and non-fossil derived aerosol particle emissions. 相似文献