二次轨道相互作用提高了Diels-Alder循环添加物中的基的反应性
Brian J Levandowski1, Dennis Svatunek1,2, Barbara Sohr2
1Department of Chemistry and Biochemistry , University of California, Los Angeles , Los Angeles , California 90095 , United States.
Journal of the American Chemical Society
|January 30, 2019
概括
在反向电子需求的迪尔斯-阿尔德反应中,跨循环 octene (TCO) 和endo-bicyclo[6.1.0]nonyne (BCN) 呈现出不同的反应性. 由于高HOMO能量,TCO与四素反应更快,而 BCN通过二次轨道相互作用显示出更大的反应性.
科学领域:
- 有机化学
- 化学动力学
- 反应机制
背景情况:
- 逆电子需求迪尔斯-阿尔德反应 (IEDDA) 对于生物对角化学至关重要.
- 压力促成的IEDDA反应具有独特的反应性.
- 了解替代剂和应变对IEDDA动力学的影响对于反应设计至关重要.
研究的目的:
- 在IEDDA反应中研究转环子 (TCO) 和内环[6.1.0]nonyne (BCN) 的比较反应性.
- 阐明了与各种二烯化合物的TCO和BCN之间观察到的反应性差异的因素.
- 探索分子轨道能量和二次轨道相互作用在决定反应速率中的作用.
主要方法:
- 分子轨道能量的计算分析 (HOMO,LUMO).
- 涉及TCO和 BCN与氨酸,环氨酸和正氨酸的IEDDA反应的动力学研究.
- 反应机制的分析,包括扭曲效应和二次轨道相互作用.
主要成果:
- 由于TCO的高HOMO能量和减少的四变形,四反应有利于TCO而不是BCN.
- TCO 和 BCN 与环二烯具有相似的反应性,这表明它们的反应率决定因素不同.
- 由于 BCN 的 HOMO-1 和 diene 的 LUMO 的二次轨道相互作用, BCN 的反应性明显高于 TCO 的反应性.
结论:
- IEDDA反应中的反应性受到包括二氧化HOMO能量,环应变和二次轨道相互作用在内的因素的组合的影响.
- 选择二氧化物 (TCO与 BCN) 和二氧化物决定了控制反应动学的主要因素.
- 二次轨道相互作用在特定的IEDDA反应中起着重要作用,例如BCN与ortho-benzoquinone的循环添加.
相关概念视频
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The Diels–Alder reaction is thermally reversible, meaning that the reaction reverts to the starting diene and dienophile under suitable temperatures. The forward reaction gives a cyclohexene derivative and is favored at low to medium temperatures. The reverse process, also called retro-Diels–Alder reaction, is a ring-opening process favored at high temperatures.
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The Diels–Alder reaction brings together a diene and a dienophile to form a six-membered ring. Both components have unique characteristics that influence the rate of the reaction.
Characteristics of the diene
Conformation
The simplest example of a diene is 1,3-butadiene, an acyclic conjugated π system. At room temperature, the molecule exists as a mixture of s-cis and s-trans conformers by virtue of rotation around the carbon–carbon single bond. Although the s-trans isomer is more stable,...
Characteristics of the diene
Conformation
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Characteristics of Dienophiles
Generally, the best dienophiles are alkenes containing electron-withdrawing substituents such as carbonyl, nitrile, and nitro groups. The feasibility of a Diels–Alder reaction depends...
Characteristics of Dienophiles
Generally, the best dienophiles are alkenes containing electron-withdrawing substituents such as carbonyl, nitrile, and nitro groups. The feasibility of a Diels–Alder reaction depends...
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01:28Diels–Alder Reaction Forming Cyclic Products: Stereochemistry
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The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.
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01:29Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
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Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
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