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81.
Koichi Kan Jinfeng Yang Kimihiro Norizawa Takafumi Kondoh Yoichi Yoshida Atsushi Ogata 《Radiation Physics and Chemistry》2011,80(12):1323-1326
A novel method to generate high-power THz radiation is proposed. If a beam with a bunch length on the order of 100 fs is injected into an electron–hole plasma of a semiconductor with a plasma frequency on the order of THz, THz wake fields are coherently generated. If the beam moves on the axis of a hollow tube covered by a metal, the frequency spectrum of the radiation is composed of discrete components. Monochromatic radiation is obtained by making only the lowest frequency component coherent. 相似文献
82.
The C16-C28 fragment common to the cytotoxic macrolide ammocidin D has been prepared by a stereospecific 5-exo closure of a γ,δ-epoxyketone followed by a rearrangement to a pyran acetal. The reaction pathway was traced by (18)O labeling of the keto carbonyl and observation of (18)O induced (13)C shifts in the pyran acetal product. NMR data of the synthetic C16-C28 fragment compared favorably to the natural product providing support of the assigned stereochemistry. 相似文献
83.
Enantioenriched synthesis of cyclopropenes with a quaternary stereocenter, versatile building blocks
Uehara M Suematsu H Yasutomi Y Katsuki T 《Journal of the American Chemical Society》2011,133(2):170-171
Ir(salen) complexes were found to catalyze enantioselective cyclopropenation efficiently. Cyclopropenation can be carried out using either a donor/acceptor- or an acceptor/acceptor-substituted diazo compound such as α-aryl-α-diazoacetates, α-phenyl-α-diazophosphonate, 2,2,2-trifluoro-1-phenyl-1-diazoethane, and α-cyano-α-diazoacetamide as carbenoid precursors. The reactions provide highly enantioenriched cyclopropenes (84-98% ee) with a functionalized quaternary carbon as versatile building blocks. 相似文献
84.
Iwasaki Y Matsui R Suzuki T Nakazaki A Kobayashi S 《Chemical & pharmaceutical bulletin》2011,59(4):522-524
We have developed a high-yielding and stereoselective vinylogous Mukaiyama aldol reaction (VMAR) of α-haloenals. Contrary to the simple α,β-unsaturated aldehyde, α-haloenals were found to be reactive affording the corresponding VMAR adducts in excellent yields. Some transformations of VMAR adducts by Pd-mediated cross-coupling were also examined in order to demonstrate the synthetic utility of VMAR of α-haloenals. 相似文献
85.
Amaya T Hifumi M Okada M Shimizu Y Moriuchi T Segawa K Ando Y Hirao T 《The Journal of organic chemistry》2011,76(19):8049-8052
Oxosumanenes were synthesized through benzylic oxidation. The electronic and redox properties were revealed to exhibit the expanded π-conjugation compared to sumanene. Single-crystal X-ray analysis of monooxosumanene showed columnar π-stacking in a concave-convex fashion. Stereoselective trimethylation of the trioxo derivative was performed via 1,2-addition to the carbonyl groups. 相似文献
86.
Saeki A Yamamoto N Yoshida Y Kozawa T 《The journal of physical chemistry. A》2011,115(36):10166-10173
Dynamics of radical cations and electrons in an admixture of a linear saturated hydrocarbon (n-dodecane) and halocarbon (carbon tetrachloride, CCl(4)) were investigated by picosecond electron beam pulse radiolysis. The decay of thermalized electrons (e(th)(-)) observed in infrared transient photoabsorption were simply accelerated by the addition of CCl(4), giving a high rate constant of 2.3 × 10(11) mol(-1) dm(3) s(-1). The decrease of the initial yield of e(th)(-) was quantified by C(37) (50 mmol), which is linked to the reaction of epithermal electrons (e(-)) with CCl(4). In contrast, the n-dodecane radical cation (RH(2)(?+)) monitored in the near-infrared indicated a convex-type dependence of the decay rate on CCl(4) concentration, although the initial yield of RH(2)(?+) remained almost constant up to a much higher CCl(4) concentration. The decay of RH(2)(?+) was analyzed by Monte Carlo simulations of geminate ion recombination with e(th)(-), chlorine anion (Cl(-)) formed via dissociative electron attachment, and CCl(4) radical anion. The results showed a good agreement with the experiments by considering two assumptions: (1) CCl(4) radical anion formed via e(th)(-) attachment and (2) narrowing of the initial distribution of Cl(-). The decrease in the initial yield of RH(2)(?+) at high CCl(4) concentration was well explained by immediate decomposition of CCl(4)(?+) to CCl(3)(+) and hole transfer from CCl(4)(?+) to adjacent RH(2) without diffusive motion of the reactants. Time-dependent density functional theory supported the spectroscopic assignment of intermediate species in the n-dodecane/CCl(4) system. The present results would be of help in understanding the electron capture reaction in multicomponent systems such as a chemically amplified resist in lithography. 相似文献
87.
88.
89.
Yoichi Sakai Ryo Omatsuzawa Iwao Sakazaki Sayaka Suzuki Hayato Hashino Takanobu Saito Takahiko Iriyama 《Hyperfine Interactions》2005,166(1-4):483-487
Samarium–iron intermetallic compounds were prepared by a melt spinning method with low and high wheel speeds, which resulted in a Th2Zn17-type and a TbCu7-type structure, respectively. Structure comparison between these types was investigated for Sm–Fe intermetallic compounds and their nitrides by 57Fe-Mössbauer spectroscopy. 相似文献
90.
Nigel Ribeiro Denis Heissler Anne Marie Albrecht-Gary Mari Gotoh Yoichi Nakatani Guy Ourisson 《Tetrahedron》2007,63(16):3395-3407
Cholesterol plays the role of membrane reinforcer in eukaryotes, whereas hopanoids play the same role in bacteria. Which components could have reinforced ‘primitive’ membranes? We describe here an efficient biomimetic synthesis of bi- and tri-cyclopolyprenols and demonstrate that these compounds reinforce the membranes of polyprenyl phosphate, which we speculated as ‘primitive’ membranes. 相似文献