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21.
Lewis acids such as ZrCl(4) or HfCl(4) catalyze the hydrostannation of acetylenes 1 by tributyltin hydride to produce the cis vinylstannanes 2 by regio- and stereoselective anti-hydrostannation. The hydrostannation of acetylenes using dibutyltin dihydride was also catalyzed by ZrCl(4) to give the stereodefined Z-Z divinyltin derivatives 4 by an anti-hydrostannation pathway. The use of nonpolar solvents such as toluene or hexane was essential for obtaining high stereoselectivity and chemical yield. Since ZrCl(4) and HfCl(4) are not soluble in such solvents, the hydrostannations were carried out in a heterogeneous system. The reactions of internal acetylenes with Bu(3)SnH proceeded smoothly, although the use of stoichiometric amounts of ZrCl(4) gave better results. The ZrCl(4)-catalyzed hydrostannation at 0 degrees C gave better yields and stereoselectivities than the reaction at room temperature. To help clalify the reason, the reaction of Bu(3)SnH with ZrCl(4) was monitored by (1)H and (119)Sn NMR spectroscopy, and it was found that Bu(3)SnH reacted with ZrCl(4) at room temperature to afford a mixture of tributyltin hydride, dibutyltin dihydride, and tetrabutyltin. 相似文献
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Mixed-metal sulfido cluster [(PdCl2)(Cp*Ir)2(μ3-S)2] (Cp*=η5-C5Me5) dissolved in CH2Cl2 reacted with two equivalent of L (L=nicotinamide, isonicotinamide, or N-methylnicotinamide) in the presence of AgBF4 to give the cationic clusters [(PdL2)(Cp*Ir)2(μ3-S)2][BF4]2. The single-crystal X-ray diffraction studies of these products have disclosed that in the solid state the PdIr2S2 cores are self-assembled to form one-dimensional chains through the intermolecular hydrogen-bonding between the amide groups for L=nicotinamide or two-dimensional sheets via the hydrogen-bonding between the amide groups and the BF4 anions for L=isonicotinamide, whereas no organization of the cluster cores is observed for L=N-methylnicotinamide. 相似文献
24.
An effective method was developed to use an enzyme in ionic liquids; the asymmetric reduction of ketones by Geotrichum candidum in ionic liquids proceeded smoothly with excellent enantioselectivity when the cell was immobilized on water-absorbing polymer containing water, while the reaction without the polymer did not proceed. 相似文献
25.
Sekino E Kumamoto T Tanaka T Ikeda T Ishikawa T 《The Journal of organic chemistry》2004,69(8):2760-2767
(-)-Quinine-catalyzed intramolecular oxo-Michael addition (IMA) of 7-hydroxy-5-methoxy-8-tigloylcoumarins was developed for the enantioselective construction of 2,3-dimethyl-4-chromanone systems in the context of the asymmetric synthesis of anti-HIV-1 active Calophyllum coumarins. Combination of the IMA and MgI(2)-assisted demethylation of the 5-methoxy group along with isomerization of the formed chromanone systems as key steps successfully led to the concise synthesis of (+)-inophyllum B and (+)-calanolide A, possible candidates for AIDS drugs. Further examination of the asymmetric IMA with cinchona alkaloids lacking a methoxy group on the quinoline skeleton suggested the influence of the methoxy substituent on stereoselectivity at the stereogenic centers of the chromanone systems. 相似文献
26.
Kosaka T Yoneyama-Takazawa T Kubota K Matsuoka T Sato I Sasaki T Tanaka Y 《Journal of mass spectrometry : JMS》2003,38(12):1281-1287
We have developed a method for protein identification with peptide mass fingerprinting and sequence tagging using nano liquid chromatography (LC)/Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). To achieve greater sensitivity, a nanoelectrospray (nano-ES) needle packed with reversed-phase medium was used and connected to the nano-ES ion source of the FTICR mass spectrometer. To obtain peptide sequence tag information, infrared multiphoton dissociation (IRMPD) was carried out in nano-LC/FTICR-MS analysis. The analysis involves alternating nano-ES/FTICR-MS and nano-ES/IRMPD-FTICR-MS scans during a single LC run, which provides sets of parent and fragment ion masses of the proteolytic digest. The utility of this alternating-scan nano-LC/IRMPD-FTICR-MS approach was evaluated by using bovine serum albumin as a standard protein. We applied this approach to the protein identification of rat liver diacetyl-reducing enzyme. It was demonstrated that this enzyme was correctly identified as 3-alpha-hydroxysteroid dehydrogenase by the alternating-scan nano-LC/IRMPD-FTICR-MS approach with accurate peptide mass fingerprinting and peptide sequence tagging. 相似文献
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28.
Tomoko Nagao Masayoshi Isozaki Tetsuya Fujimoto Iwao Yamamoto 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8-9):1975-1976
The reaction of a cyclic phosphonium ylide [ 1 ] with enoate 2 gives a hydroazulene derivative with stereoselectivity. 相似文献
29.
The frequency domain of non-resonant two-photon ionization, defined as a frequency separation from half of the ionization energy to the excitation energy, was investigated using density functional theory calculations. Several organic compounds have the potential for use in the measurement of the ultrashort optical pulse width in the ultraviolet region using an autocorrelator consisting of a mass spectrometer as a two-photon-response detector. 相似文献
30.
Takahiro Egawa Kazuhisa Hirabayashi Dr. Yuichiro Koide Chiaki Kobayashi Dr. Naoya Takahashi Dr. Tomoko Mineno Dr. Takuya Terai Dr. Tasuku Ueno Dr. Toru Komatsu Dr. Yuji Ikegaya Prof. Norio Matsuki Prof. Tetsuo Nagano Dr. Kenjiro Hanaoka 《Angewandte Chemie (International ed. in English)》2013,52(14):3874-3877