共查询到13条相似文献,搜索用时 62 毫秒
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利用半经验分子轨道理论AM1方法,研究了5-亚甲基-1,3-二噁烷-4,6-二酮与亚甲基烯酮的2,3-位C=C,3,4-位C=O和1,2-位C=O三种双键位置上的环加成反应的反应机理.采用Berny梯度法优化得到反应的过渡态,并进行了振动分析确认.计算结果表明,环加成反应是按照协同的非同步途径进行的,经过一个扭曲的六员环过渡态,前线轨道分析表明反应机理为[4+2]机理.根据AM1优化得到的产物反应物及过渡态的生成热可知三个反应的活化焓分别为27.07kJ·mol-1,32.41kJ·mol-1和137.96kJ·mol-1,2,3-位C=C双键上的环加成反应的活化焓最低,这与实验中只观察到2,3-位C=C双键上环加成产物的结论是一致的. 相似文献
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The direct iodination of polyfluorinated vinyl stannanes by tin-iodine exchange methodology was achieved giving (Z)-α-fluoro-β-trifluoromethyl vinyl iodides stereospecifically. Changing the substituent in R group from the electron-withdrawing group to electron-donating group led to an increase in the yield from 78% to 90%, while it was moved from para to meta position the reaction did not afford a dramatic change in the yield (90% to 95%). In addition, this reaction also can be applied to the vinyl stannane with heterocyclic group. The further coupling reaction of prepared vinyl iodide containing heterocyclic moiety with (Z)-α-fluoro-β-trifluoromethylstannanes gave polyfluorinated heterocyclic alkadienes with 2E,4E-selectivity. 相似文献
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报道了一种高效的δ-三氟甲基-δ-芳基-取代对亚甲基苯醌的叠氮化芳基化反应. 以Na2CO3为催化剂, 叠氮三甲基硅烷与δ-三氟甲基-δ-芳基取代对亚甲基苯醌发生1,6-共轭加成反应, 以优异的分离产率(90%~96%)获得了结构多样的含有三氟甲基和叠氮取代的二芳基甲烷化合物.该反应具有良好的底物适用范围和官能团兼容性. 相似文献
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可修饰的内酯,α-氯甲基-α-甲基-β-丙内酯的合成和聚合*王明霞李子臣贺晓晖杨丽**李福绵(北京大学化学系北京100871)关键词α-氯甲基-α-甲基-β-丙内酯,开环聚合*1995-02-20收稿;1996-03-12修回:自然科学基金课题;**... 相似文献
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5-烃基-2,3-二甲基吡嗪N-单氧化物的合成 总被引:1,自引:0,他引:1
一烃基或二烃基吡嗪的N-单氧化物可以进行氯化、乙酰氧基化等反应,它是重要的有机合成中间体.据报道二烃基吡嗪与30%过氧化氢在醋酸中进行N-氧化反应,当二烃基吡嗪:30%过氧化氢:醋酸的摩尔比为1:2:5、反应温度70~80℃、反应时间8h时,产物是N-单氧化物;当摩尔比为1:4:10、反应温度95℃、反应时间8~24h时,产物是N-二氧 相似文献
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A combination of iterative Jacobsen’s hydrolytic kinetic resolution and reduction of a ketone for the construction of a 1,3-polyol moiety are key steps en route to a total synthesis of (+)-cryptocarya diacetate. 相似文献
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Christina Matsingou 《Thermochimica Acta》2007,452(2):116-123
Differential scanning calorimetry (DSC) was used to study the effect of cholesterol on the perturbation of DPPC bilayers induced by eight bioactive structurally related labdanes isolated from the resin ‘ladano’ of Cistus creticus subsp. creticus (Cistaceae) or semisynthesized from the mother compounds. Labdanes themselves induced profound modifications in DPPC bilayer organization and thermotropic properties that were altered when cholesterol was incorporated in equimolar amounts to the labdanes. The present work shows that, up to 10 mol% of the equimolar mixture of cholesterol and the labdanes, the modifications evoked on DPPC bilayer organization are in accordance to these induced by the labdanes themselves. When the concentration exceeded 20 mol%, cholesterol influence dominated while the effect of the labdanes was suppressed and their interaction with the bilayer was probably prevented. The degree by which cholesterol modulated the labdane interaction with the bilayer depended on their structural characteristics that determine their localization in the bilayer interior. Polar groups that force the labdanes to localize themselves at the interfacial region broadened the concentration range by which labdanes interacted with the DPPC bilayer even in the presence of high concentration of cholesterol where cholesterol-rich domains are preferentially formed. On the other hand, labdanes possessing functional groups that promote their deeper penetration in the bilayer interior compete with cholesterol in a high extent for the same localization sites resulting in their possible elimination from the bilayer when the concentration of cholesterol present exceeds the 20 mol%. 相似文献
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《Arabian Journal of Chemistry》2022,15(7):103892
The purpose of this study was to illustrate the mechanism of “enzyme inactivation and toxicity reduction” of Fructus Tribuli (FT) after being heating processed. Ultra-high performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (UHPLC-MS/MS) was used to quantitatively analyze the contents of four steroidal saponins in crude Fructus Tribuli (CFT) and stir-fried Fructus Tribuli (SFT) under different storage times at room temperature. The enzyme activity of β-D-glucosidase in CFT and SFT were determined and calculated by ultraviolet–visible spectrometry (UV-VIS spectrometry). In addition, the enzyme hydrolysates of FOT and tribuluside A were qualitatively analyzed by ultra-high-performance liquid chromatography coupled with quadruple-time-of-flight mass spectrometry (UHPLC-Q-TOF/MS). The hepatorenal toxicity of spirostanol saponins in FT were further confirmed by in vivo and in vitro experiment. This study confirmed that “enzyme inactivation and toxicity reduction” was one of the reasons why the stir-frying can reduce hepatorenal toxicity of FT, and further enriched the exploration on the mechanism of processing toxicity reduction. 相似文献