使用立体选择性迪尔斯-阿尔德循环添加来检测烯-烯相互作用中的替代物效应
Steven E Wheeler1, Anne J McNeil, Peter Müller
1Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA.
Journal of the American Chemical Society
|February 18, 2010
概括
使用迪尔斯-阿尔德反应,探索了-三明治复合物的替代效应. 结果显示,pi-stacking相互作用,而不是pi-system捐赠,驱动这些效应,挑战现有模型.
科学领域:
- 有机金属化学 有机金属化学
- 超分子化学 超分子化学
- 物理有机化学 有机化学
背景情况:
- 在超分子化学和有机金属复合体中,aryl-aryl相互作用至关重要.
- 了解这些相互作用的替代物效应是设计分子系统的关键.
- 之前的模型往往专注于pi系统电子效果.
研究的目的:
- 研究涉及-三明治复合物的立体选择性迪尔斯-阿尔德反应的替代效应.
- 阐明pi堆叠相互作用与电子效应在调解这些替代效应中的作用.
- 通过实验推导出相对pi-stacking的自由能量,并将它们与替代物属性相关联.
主要方法:
- 实验迪尔斯-阿尔德循环添加来探测立体选择性.
- 过渡状态和pi-stacking相互作用的计算建模.
- 分析产品分布以确定自由能量差异.
- 实验数据与哈梅特西格玛常数的相关性.
主要成果:
- 立体选择性是通过在竞争过渡状态中的差异性pi堆叠相互作用来调解的.
- 实验中的pi-stacking自由能量与哈梅特 (r = 0.96) 常数 (r = 0.96) 有很好的相关性.
- 在气相计算中,分散效应被发现是微不足道的,与之前的实验保持一致.
- 结果表明,OMe增强了pi堆叠,与依赖于pi系统偏振的模型相矛盾.
结论:
- 阿里尔-阿里尔三明治复合体中的替代效应主要由穿越空间的相互作用来决定,而不是pi系统的电子捐赠.
- 这些发现挑战了在-相互作用中替代物效应的既定模型.
- 这项研究提供了第一个实验证据,表明像OMe这样的电子捐赠小组可以增强pi堆叠相互作用.
相关概念视频
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry
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.
Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
Diels–Alder Reaction: Characteristics of Dienophiles
In a Diels–Alder reaction, the diene is usually an electron-rich system and acts as a nucleophile, whereas the dienophile is electron-deficient and functions as an electrophile. Much like the diene, the nature of the dienophile significantly impacts the outcome of the reaction.
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 on...
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 on...
Diels–Alder Reaction: Characteristics of Dienes
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, the...
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, the...
Cycloaddition Reactions: Overview
Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.


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