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排序方式: 共有549条查询结果,搜索用时 31 毫秒
21.
22.
Lee K Kim H Miura T Kiyota K Kusama H Kim S Iwasawa N Lee PH 《Journal of the American Chemical Society》2003,125(32):9682-9688
3-tert-Butyldimethylsilyloxyalk-2-enylsulfonium salts, generated in situ from the reaction of alpha,beta-enones with dimethyl sulfide in the presence of TBSOTf, underwent a novel nucleophilic substitution with allylindiums to give silyl enol ethers of delta,epsilon-alkenyl ketones in good yields, which correspond to formal Michael addition products. In a similar manner, 1,4-propargylation of propargylindiums onto the sulfonium salts produced the corresponding silyl enol ethers of delta,epsilon-alkynyl ketones in good yields. Organoindium reagents derived from gamma-substituted propargyl bromide and indium afforded the corresponding silyl enol ethers of beta-allenyl ketones in good yields. The reaction proceeds via an addition-substitution mechanism involving the formation of allylic sulfonium salts. The presence of the intermediate sulfonium salt was confirmed by observation of the low-temperature (1)H NMR spectra. 相似文献
23.
[reaction: see text] Phosphates from 3-substituted 4,4,4-trifluorobut-2-en-1-ols were found to be effective for construction of CF3-containing quaternary carbon centers by way of Cu(I)-catalyzed Grignard reactions in the presence of catalytic amounts of CuCN and trimethylsilyl chloride (TMSCl) in an anti S(N)2' manner. 相似文献
24.
Nobuo Ishikawa Tomoya Kitazume Kunitake Chino Mohamed El-Said Mustafa 《Journal of fluorine chemistry》1981,18(4):447-457
The reactions of -2-methyl-2-pentene (1) with several - difunctional benzenes afforded eight- and nine-membered benzoheterocyclic compounds carrying perfluoroalkyl groups. Salicylic acid, salicylaldehyde, and their methyl or chloro derivatives reacted in triethylamine-acetonitrile system giving perfluoroalkylated 2H,6H-1,5-benzodioxocin-2,6-dione (8) and 4H,6H-1,5-benzodioxocin (9) compounds respectively, while phthalyl alcohol and o-hydroxyphenethyl alcohol in triethylamine-diethyl ether system gave perfluoroalkylated 1H,3H,7H-2,6- and 4H,6H,7H-1,5-benzodioxonin compounds, (10) and (11). o-Aminobenzyl alcohol and (1) in diethyl ether afforded a perfluoroalkylated benzoxazocinobenzoxazocinone compound (15). 相似文献
25.
Tatsuhiko Kashimura Tomoya Ikezaki Yusuke Ohta Satoshi Yabushita 《Journal of computational chemistry》2019,40(2):482-499
One of the most spectacular yet unsolved problems for the ICN -band photodissociation is the non-statistical spin-rotation F1 = N + 1/2 and F2 = N − 1/2 populations for each rotation level N of the CN fragment. The F1/F2 population difference function f(N) exhibits strong N and λ dependences with an oscillatory behavior. Such details were found to critically depend on the number of open-channel product states, namely, whether both I (2P3/2) and I (2P1/2) are energetically available or not as the dissociation partner. First, in the asymptotic region, the exchange and dipole-quadrupole inter-fragment interactions were studied in detail. Then, as the diabatic basis, we took the appropriate symmetry adapted products of the electronic and rotational wavefunctions for the F1 and F2 levels at the dissociation limits. We found that the adiabatic Hamiltonian exhibits Rosen–Zener–Demkov type nonadiabatic transitions reflecting the switch between the exchange interaction and the small but finite spin-rotation interaction within CN at the asymptotic region. This non-crossing type nonadiabatic transition occurs with the probability 1/2, that is, at the diabatic limit through a sudden switch of the quantization axis for CN spin S from the dissociation axis to the CN rotation axis N . We have derived semiclassical formulae for f(N) and the orientation parameters with a two-state model including the 3A′ and 4A′ electronic states, and with a four-state model including the 3A′ through 6A′ electronic states. These two kinds of interfering models explain general features of the F1 and F2 level populations observed by Zare's group and Hall's group, respectively. © 2018 Wiley Periodicals, Inc. 相似文献
26.
A novel carbonyl alkynylation has been accomplished based on utilization of the Meerwein-Ponndorf-Verley (MPV) reaction system. The success of the MPV alkynylation crucially depends on the discovery of the remarkable ligand acceleration effect of 2,2'-biphenol. For example, the alkynylation of chloral (2c) with the aluminium alkoxide 6(R = Ph), prepared in situ from Me(3)Al, 2,2'-biphenol and 2-methyl-4-phenyl-3-butyn-2-ol (1a) as an alkynyl source, proceeded smoothly in CH(2)Cl(2) at room temperature to give the desired propargyl alcohol 3ca in almost quantitative yield after 5 h stirring. The characteristic feature of this new transformation involving no metal alkynides can be visualized by the fact that the alkynyl group bearing keto carbonyl was transferred successfully to aldehyde carbonyl without any side reactions on keto carbonyl. Although the use of (S)-1,1[prime or minute]-bi-2-naphthol and its simple analogues was found to be unsuitable for inducing asymmetry in this reaction, design of new chiral biphenols bearing a certain flexibility of the biphenyl axis led to satisfactory results in terms of enantioselectivity as well as reactivity. 相似文献
27.
[reaction: see text] Indium-mediated allenylation of alpha,beta-unsaturated ketones in the presence of tert-butyldimethylsilyl triflate and dimethyl sulfide gives 6-siloxy-1,2,5-trienes, which undergo W(CO)(5)(L)-catalyzed 5-endo cyclization to give the corresponding cyclopentene derivatives in good yield. Furthermore, this novel W(CO)(5)(L)-catalyzed cyclization of allenyl silyl enol ethers proceeds in a 6-endo manner when 5-siloxy-1,2,5-trienes are employed as a substrate. In these reactions, effective electrophilic activation of allenyl compounds for attack by silyl enol ethers is achieved using a catalytic amount of W(CO)(6). 相似文献
28.
Oishi T Hagiwara K Kinumi T Yamakawa Y Nishijima M Nakamura K Arimoto H 《Organic & biomolecular chemistry》2003,1(15):2626-2629
The effects of Soto's 'beta-sheet breaker peptide' and its polymer on PrPSc formation in ScN2a cells were investigated. Surface plasmon resonance study indicated that direct binding between PrP(81-145) and the 'beta-sheet breaker peptide' is not specific and may not play a major role in the inhibition of PrPSc formation. 相似文献
29.
30.
Yoshiki Horikawa Naoya Konakahara Tomoya Imai Abe Kentaro Yoshinori Kobayashi Junji Sugiyama 《Polymer Degradation and Stability》2013
The enzymatic hydrolysis of cellulose I achieves almost complete digestion when sufficient enzyme loading as much as 20 mg/g-substrate is applied. However, the yield of digestion reaches the limit when the enzyme dosage is decreased to 2 mg/g-substrate. Therefore, we have performed three pretreatments such as mercerization, dissolution into phosphoric acid and EDA treatment. Transformation into cellulose II hydrate by mercerization and dissolution into phosphoric acid were not sufficient because substrate changed to highly crystalline structure during saccharification. On the other hand, in the case of crystalline conversion of cellulose I to IIII by EDA, almost perfect digestion was achieved even in enzyme loading as small as 0.5 mg/g-substrate, furthermore, hydrolyzed residue was typical cellulose I. The structural analysis of substrate after saccharification provides an insight into relationships between cellulose crystalline property and cellulase toward better enzymatic digestion. 相似文献