7-d-和8-d-双循环[4.2.0]oct-2-的热反应
John E Baldwin1, Phyllis A Leber, David C Powers
1Department of Chemistry, Syracuse University, Syracuse, New York 13244, USA. jbaldwin@syr.edu
Journal of the American Chemical Society
|August 3, 2006
概括
双环[4.2.0]oct-2-ene的热反应显示C1-C8键同解,形成一个稳定的二基中间体. 这条路径,而不是轨道对称性,决定了[1,3]碳转移的立体化学.
科学领域:
- 有机化学 有机化学
- 反应机制 反应机制
- 物理有机化学 有机化学
背景情况:
- 研究Bicyclo[4.2.0]oct-2-ene及其乳标记的类似物,以了解热反应途径.
- 之前对bicyclo[3.2.0]hept-2-ene类型的研究提供了对观察到的转化进行比较的背景.
研究的目的:
- 在300°C时动力学研究bicyclo[4.2.0]oct-2-ene及其化类型的气相热反应.
- 阐明反应机制,包括键裂变,表皮化和碳迁移途径.
主要方法:
- 气相色谱 (GC) 用于运动分析.
- 核磁共振 (2H NMR) 光谱仪用于结构阐明.
- 在气相中300°C的动力学研究.
主要成果:
- 没有观察到C1-C6键裂解反应,与bicyclo[3.2.0]hept-2-ene系统不同.
- 在C8的表皮化比[1,3]碳转移以形成双循环[2.2.2]oct-2-ene.明显更快.
- 对于 [1,3] 碳迁移与反转与保留的速率常数的比率约为1.4.
- C1-C8键的同解产生了一种寿命长,形状灵活的二基中间体.
结论:
- 观察到的反应模式与二极端中间路径一致.
- 在这个系统中,轨道对称性并不控制[1,3]西格马热碳转移的立体化学.
- 双根中间体允许多个反应途径,包括C1-C8键的重构,碎片化和碳迁移,具有不同的立体化学.
相关概念视频
Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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.
[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 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.
Cycloaddition Reactions: MO Requirements for Thermal Activation
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.


