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首页> 外文期刊>Chemistry: A European journal >The stepwise Diels-Alder reaction of 4-nitrobenzodifuroxan with Danishefsky's diene
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The stepwise Diels-Alder reaction of 4-nitrobenzodifuroxan with Danishefsky's diene

机译：4-硝基苯并二呋喃毒素与Danishefsky二烯的逐步导液反应

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摘要

The Diels-Alder reaction of 4-nitrobenzodifuroxan (NBDF) with 1-methoxy-3-trimethylsilyloxy-1,3-butadiene has been investigated experimentally and theoretically. Treatment of NBDF with excess diene in chloroform at room temperature was found to afford a single product that contained a carbonyl functionality. Based on an X-ray structure and NMR spectroscopic data, the product appeared to be a result of the hydrolysis of the OSiMe_3 moiety of the thermodynamically more stable endo [2+4] cycloadduct, characterized by a cis arrangement of the MeO and NO_2 functionalities. In situ NMR investigations of the interaction were carried out at room temperature in CDCl_3 and at -40 °C in deuterated acetonitrile. Calculations at the B3LYP/6-31G* level in the gas phase and in acetonitrile were carried out under the assumption that the most stable cis conformation of the diene is also the most reactive in the interaction. The analysis revealed the NBDF/cis diene interaction involves the formation of a zwitterionic intermediate. Importantly, this intermediate is formed in two preferred conformations, which correspond to the endo and exo modes of approach of the reagents. Cyclization of these two identified conformations afforded the experimentally characterized endo and exo [2+4] cycloadducts. According to the calculations, the interconversion of the two conformers can either take place through a return to the pre-reaction complexes or it can occur by rotation through an intermediate conformation of lesser stability. In view of the stepwise character of the interaction, the possibility that the intermediate zwitterion is the result of the interaction between NBDF and the trans diene could not be excluded. Calculations carried out with the most stable and more populated s-trans conformer confirmed this idea and supported the role of the zwitterion in the overall interaction.
机译：通过实验和理论地研究了4-硝基苯并二呋罗氧基（NBDF）与1-甲氧基-3-三甲基甲硅烷基甲硅烷基-1,3-丁二烯的DIELS- ald反应。发现室温下氯仿过量二烯的NBDF的NBDF得到一种包含碳基官能度的单一产物。基于X射线结构和NMR光谱数据，该产物似乎是热力学上更稳定的内部[2 + 4]环形化学的osime_3部分的水解的结果，其特征在于MEO和NO_2功能的顺便说明。原位NMR研究在CdCl_3的室温下进行相互作用，在-40℃下进行氘代乙腈。在气相和乙腈中的B3Lyp / 6-31g *水平的计算在假设中，二烯的最稳定的顺式构象也是相互作用中最具反应性的。该分析显示NBDF / CIS二烯相互作用涉及形成两性离子中间体。重要的是，该中间体形成在两个优选的构象中，其对应于试剂的endo和exo方法。这两个鉴定的构象的环化提供了实验表征的endo和Exo [2 + 4]环形化学。根据计算，两种塑造剂的互连可以通过返回到预反应复合物进行，或者可以通过旋转通过较小稳定性的中间构象而发生。鉴于相互作用的逐步特征，中间两性周是NBDF与反式二烯之间的相互作用的结果的可能性无法排除。用最稳定和更具填充的S-Trans Conformer进行的计算证实了这种想法并支持两性周在整体相互作用中的作用。

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