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51.
Yoshiharu Abe Toshio Masuda Toshinobu Higashimura 《Journal of polymer science. Part A, Polymer chemistry》1989,27(13):4267-4279
(o-Methylphenyl)acetylene polymerized with high yields in the presence of W and Mo catalysts. W catalysts were more active than the corresponding Mo catalysts. The weight-average molecular weight of the polymer formed with W(CO)6–CCl4–hv reached 8 × 105, being higher than the maximum value (ca. 2 × 105) for poly(phenylacetylene). The polymer had the structure $\rlap{--} [{\rm CH} \hbox{=\hskip-1pt=} {\rm C}(o - {\rm CH}_3 {\rm C}_6 {\rm H}_4 )\rlap{--} ]_n $. The stereochemical structure of the main chain could be determined by 13C-NMR; the cis content varied in a range of 41–61% depending on the polymerization conditions. The present polymer was thermally more stable than poly(phenylacetylene) according to thermogravimetric analysis. Interestingly, this polymer possessed deeper color than poly(phenylacetylene), and showed a fairly strong absorption in the visible region. 相似文献
52.
Toshio Yamanaka Mitsuru Ohkubo Fumie Takahashi Masayuki Kato 《Tetrahedron letters》2004,45(13):2843-2845
An efficient synthesis of the orally-active GpIIb/IIIa antagonist FR184764 was achieved. The key intermediate, an optically active ethynyl β-amino ester, was synthesized efficiently by utilizing a lipase catalyzed kinetic resolution step. 相似文献
53.
Kasai HF Tsubuki M Matsumoto Y Shirao M Takahashi K Honda T Ueda H 《Chemical & pharmaceutical bulletin》2004,52(3):311-315
Gas chromatographic separations of the stereoisomers of menthol derivatives, important intermediates in the synthesis of physiologically active natural products, were carried out on several substituted beta-cyclodextrin (CD) columns, including per-O-methyl-beta-cyclodextrin (PME-beta-CD), heptakis(2,3-di-O-acetyl-6-tert-butyldimethylsilyl)-beta-CD (DIAC-6-TBDS-beta-CD), and heptakis(2,3-di-O-methyl-6-tert-butyldimethylsilyl)-beta-CD (DIME-6-TBDS-beta-CD) as chiral stationary phases (CSPs). With the DIME-6-TBDS-beta-CD column, a separation of the Z- and E-isomers of methylidenementhol was accomplished; no separation was achieved with the other columns. The stereoisomers of methylidenementhol and the corresponding tert-butyldimethylsilyl (TBS) ether were separated on both the beta-CD and the heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TME-beta-CD) columns by high-performance liquid chromatography (HPLC) with a mobile phase involving acetonitrile and H(2)O. For the separation of the Z- and E-isomers of methylidenementhol, the TME-beta-CD column was superior. In contrast, the beta-CD column was preferable in the case of the corresponding TBS ether. 相似文献
54.
Treatment of 1-chlorovinyl p-tolyl sulfoxides, prepared from ketones and chloromethyl p-tolyl sulfoxide, with N-lithio arylamines resulted in the formation of sulfinylaziridines in good to high yields. The sulfinylaziridines were treated with N-lithio aniline or N-lithio p-chloroaniline to afford α-quaternary α-amino aldehydes in good yields. From α-quaternary α-amino aldehydes, α-quaternary α-amino acid esters and β-quaternary β-amino alcohols were obtained. When optically active chloromethyl p-tolyl sulfoxide was used in this procedure, a method for the synthesis of optically active α-quaternary α-amino aldehydes was realized. The reaction mechanism, including asymmetric induction, for the formation of the sulfinylaziridines is described. 相似文献
55.
Eguchi S Suzuki T Okawa T Matsushita Y Yashima E Okamoto Y 《The Journal of organic chemistry》1996,61(21):7316-7319
Both optical isomers of a quinazoline alkaloid, vasicinone, were synthesized by two different methods. The first method used (3S)-3-hydroxy-gamma-lactam as a chiral synthon, which was, after O-TBDMS protection, o-azidobenzoylated followed by treatment with tri-n-butylphosphine to afford (S)-(-)-vasicinone via the tandem Staudinger/intramolecualr aza-Wittig reaction. The second method utilized asymmetric oxygenation of deoxyvasicinone with (1S)-(+)- or (1R)-(-)-(10-camphorsulfonyl)oxaziridine (the Davis reagent), respectively. The aza-enolate anion of deoxyvasicinone was treated with (S)-(+)-reagent to afford (R)-(+)-vasicinone in 71% ee, while the reaction with (R)-(-)-reagent gave (S)-(-)-vasicinone in 62% ee. The optical purity was analyzed by HPLC on specially modified cellulose as a stationary phase. These results provided a facile method to prepare both optical isomers of vasicinone and confirmed the recently reversed stereochemistry of natural (-)-vasicinone. 相似文献
56.
Iwasaki T Kounosu A Uzawa T Samoilova RI Dikanov SA 《Journal of the American Chemical Society》2004,126(43):13902-13903
The weakly coupled 15N atoms around a reduced Rieske [2Fe-2S] cluster of the uniformly 15N-labeled, hyperthermostable archaeal Rieske protein appear to produce readily observable cross-peaks in the HYSCORE spectra, with the well-resolved couplings of 0.3-0.4 MHz for the Nepsilon and 1.1 MHz for the peptide backbone nitrogens, in addition to the contributions from the coordinated Ndelta atoms. These features can be used for structure-mechanism studies of the biological redox protein system involving the weakly coupled nitrogens in coupled electron-proton transfer reactions. 相似文献
57.
Moribe K Tsuchiya M Tozuka Y Yamaguchi K Oguchi T Yamamoto K 《Chemical & pharmaceutical bulletin》2004,52(5):524-529
We prepared and characterized a grinding-induced equimolar complex of thiourea with ethenzamide. When thiourea and ethenzamide were co-ground at a molar ratio of 3 : 1, new powder X-ray diffraction (PXRD) peaks were observed in addition to PXRD peaks of thiourea crystals. The optimum stoichiometry of the new structure was confirmed as 1 : 1 mol/mol. Effect of grinding time on the thiourea-ethenzamide equimolar complex formation was investigated by using PXRD, differential scanning calorimetry and Fourier transform infrared spectroscopy. The equimolar crystal structure was confirmed by X-ray diffraction measurements of the single crystal which was recrystallized from ethanol. It was found that the intermolecular hydrogen bond formations between thiourea and ethenzamide molecules contributed to the equimolar complex formation. The complex formation was not observed in the cases where benzamide, salicylamide or 3-ethoxybenzamide was co-ground with thiourea. 2-Alcoxyl benzamide structures should be required for the grinding-induced equimolar complex formation with thiourea. 相似文献
58.
[reaction: see text] Anodic intramolecular cyclization of alpha-(phenylthio)acetamides using a fluoride ion mediator was realized. Under ultrasonic irradiation, cyclization was accelerated markedly to give desired cyclized products in moderate to good yields. The local heating effect of ultrasonic irradiation seems to be more advantageous than usual heating. 相似文献
59.
Taguchi Y Ohtani H Tsuge S Ishida Y Kimura K Yoshikawa T 《Journal of chromatography. A》2003,993(1-2):137-142
Highly sensitive and specific determination of trace amounts of a polymeric hindered amine light stabilizer (HALS) in polypropylene (PP) materials could be established by improving reactive thermal desorption-gas chromatography (RTD-GC) in the presence of an organic alkali, tetramethylammonium hydroxide. By using nitrogen-phosphorus detection, highly selective detection of the HALS-related components was attained. In addition, the use of a polar poly(ethylene glycol) separation column alleviated the adsorption of minor specific pyrolysis products. This modified RTD-GC method allowed the determination of the polymeric HALS (Mr 1900) in PP even for trace concentrations between 100 and 500 ppm, through observing selectively the characteristic products containing a tetramethylpiperidine moiety, which had been impossible to detect under the previous RTD-GC conditions using a non-polar separation column and conventional flame ionization detection. 相似文献
60.
High level ab initio calculations using complete active space self-consistent field and multi reference single and double excitation configuration interaction methods with cc-pVDZ (correlation consistent polarized valence double zeta) and cc-pVTZ (triple zeta) basis sets have been performed to elucidate the reaction mechanism of the ion-molecule reaction, C2H2(1Sigmag+) + O+(4S), for which collision experiment has been performed by Chiu et al. [J. Chem. Phys. 109, 5300 (1998)]. The minor low-energy process leading to the weak spin-forbidden product C2H2+ (2Piu) + O(1D) has been studied previously and will not be discussed here. The major pathways to form charge-transfer (CT) products, C2H2+ (2Piu) + O(3P) (CT1) and C2H2+ (4A2) + O(3P) (CT2), and the covalently bound intermediates are investigated. The approach of the oxygen atom cation to acetylene goes over an energy barrier TS1 of 29 kcal/mol (relative to the reactant) and adiabatically leads the CT2 product or a weakly bound intermediate Int1 between CT2 products. This transition state TS1 is caused by the avoided crossing between the reactant and CT2 electronic states. As the C-O distance becomes shorter beyond the above intermediate, the C1 reaction pathway is energetically more favorable than the Cs pathway and goes over the second transition state TS2 of a relative energy of 39 kcal/mol. Although this TS connects diabatically to the covalent intermediate Int2, there are many states that interact adiabatically with this diabatic state and these lead to the other charge-transfer product CT1 via either of several nonadiabatic transitions. These findings are consistent with the experiment, in which charge transfer and chemical reaction products are detected above 35 and 39 kcal/mol collision energies, respectively. 相似文献