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41.
[reaction: see text] Fumarate- and acrylate-substituted oxazolidinones undergo tandem radical reaction to form dienes in moderate to good yields. The resulting dienes provide cyclooctenes in moderate to good yields after ring-closing metathesis (RCM). The role of the carbon backbone substituents and other variables in the efficiency of the eight-membered ring formation is discussed. 相似文献
42.
Chiral beta-amino esters are synthesized in one-pot from three components, amines, aldehydes, and ethyl bromoacetate, under the rhodium-catalyzed Reformatsky-type reaction condition, where complete diastereoselection is achieved in the nucleophilic addition step of ethyl bromoacetate to the imines prepared in 相似文献
43.
M. Nakagawa S. Kato H. Fukazawa Y. Hasegawa J. Miyazawa T. Hino 《Tetrahedron letters》1985,26(48):5871-5874
Oxytryptophans 3, which are readily obtained by dye-sensitized photooxygenation of tryptophan followed by acid treatment, undergo a facile N,N′-transacylation to give the 3-(2-aminophenyl)-2-pyrrolidones 4 in the absence of oxygen, whereas in the presence of oxygen 3a was oxidized to kynurenine. 相似文献
44.
45.
A. Kawasuso M. Hasegawa M. Suezawa S. Yamaguchi K. Sumino 《Hyperfine Interactions》1994,84(1):397-406
The charge state dependence of positron lifetime and trapping at divacancy (V2) in Si doped with phosphorus or boron has been studied after 15 McV electron irradiation up to a fluence of 8.0×1017 e/cm2. The positron trapping cross sections for V
2
2–
, V
2
–
and V
2
0
at 300 K were about 6×10–14, 3×10–14 and 0.1–3×10–14 cm2, respectively. For V
2
+
, however, no positron trapping was observed. The marked difference in the cross sections comes from Coulomb interaction between the positron and the charged divacancy. The trapping rates for V
2
0
and V
2
2–
have been found to increase with decreasing temperature in the temperature range of 10–300 K. These results are well interpreted by a two-stage trapping model having shallow levels with energy of 9 meV (V
2
0
) and 21 meV (V
2
2–
). The appearance of a shallow level for V
2
0
can not be explained by a conventional Rydberg state model. The lifetime (290–300 ps) in V
2
0
is nearly constant in the temperature range from 10 to 300 K, while that in V
2
2–
increases from 260 ps at 10 K to 320 ps at 300 K. The lifetime (260 ps) in V
2
2–
is shorter than that in V
2
0
at low temperature, which is due to the excess electron density in V
2
2–
. At high temperature, however, the longer lifetime of V
2
2–
than that of V
2
0
is attributed to lattice relaxation around V
2
2–
. 相似文献
46.
We analyse a scheme of transition from the Poissonian statistics for quantum levels to the Gaussian one of random matrix ensembles in the framework of level dynamics discussed by Yukawa. We propose a means of connecting these two limiting statistics by showing a result that Yukawa's parameter / of the exponential family can be efficiently replaced by the ratio <E>/<Q> which reflects directly a degree of the eigenvalue correlations of each sample matrix in the ensemble. On this basis, we discuss a correspondence between the level statistics of a generic quantum system and its classical regular/chaotic dynamics in terms of the semiclassical power spectrum and its second moment formulated by Feingold-Peres and Prosen-Robnik. We also discuss some limiting proceduresN (infinite limit of the matrix dimension) pertinent to the Gaussian ensembles, and remark about the possibility offractional power law of Brody's type. 相似文献
47.
48.
Hisahiro Hagiwara Fumihide TakeuchiTakashi Hoshi Toshio SuzukiToshihiro Hashimoto Yoshinori Asakawa 《Tetrahedron letters》2003,44(11):2305-2306
1,9-Dideoxyforskolin 2 has been synthesized starting from ptychantin A 3. 相似文献
49.
Eietsu Hasegawa Shinya Takizawa Akira Yamaguchi Naoki Chiba Hiroshi Ikeda 《Tetrahedron》2006,62(27):6581-6588
Photoinduced electron-transfer reactions of several ketone substrates were studied to evaluate the utilities of 1,6-bis(dimethylamino)pyrene (BDMAP), 1,6-dimethoxypyrene (DMP), 9,10-bis(dimethylamino)anthracene (BDMAA), and 9,10-dimethoxyanthracene (DMA) as electron-donating sensitizers cooperating with 2-aryl-1,3-dimethylbenzimidazolines. BDMAP and DMP generally led higher conversion of ketones and better yield of reduction products compared to BDMAA and DMA. 相似文献
50.