7-d-および8-d-ビサイクロ[4.2.0]オクト-2-エネスの熱反応
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
まとめ
バイサイクロ[4.2.0]オクト-2-エンの熱反応では,C1-C8結合の同解が示され,安定した二基間物質が形成されます. この経路は,軌道対称性ではなく, [1,3] 炭素シフトのステレオ化学を決定する.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 反応メカニズム 反応メカニズム
- 物理有機化学 物理有機化学
背景:
- Bicyclo[4.2.0]oct-2-eneとそのデュテリウムラベル付のアナログは,熱反応経路を理解するために研究されています.
- ビサイクロ[3.2.0]ヘプト-2-エネの類似体に関する以前の研究は,観察された変異の比較的な文脈を提供します.
研究 の 目的:
- 300°Cでのビサイクロ[4.2.0]オクト-2-エネおよびそのデュテラートアナログのガス相熱反応を動態学的に調査する.
- 結合割れ,エピメリゼーション,炭素移動経路を含む反応機構の解明.
主な方法:
- 運動分析のためのガスクロマトグラフィー (GC).
- デウテリウム核磁気共鳴 (2H NMR) スペクトロスコピーは,構造の解明のためのものです.
- ガス相における300°Cでの運動研究.
主要な成果:
- ビサイクロ[3.2.0]ヘプト-2-エネ系とは異なり,C1-C6結合分裂反応は観察されなかった.
- C8でのエピメリゼーションは, [1,3] の炭素シフトより,バイサイクロ[2.2.2]オクト-2-エネを形成するシフトよりも,著しく速かった.
- 逆転対保持による[1,3]炭素移動の速度常数の比率は約1.4であった.
- C1-C8結合の同解により,長寿で,形状的に柔軟な二基中間物質が生成されます.
結論:
- 観測された反応パターンは,ダイラジカル中間経路と一致しています.
- 軌道の対称性は,このシステムの [1,3] シグマトロピック炭素シフトのステレオ化学を制御しない.
- ダイラジカル中間物質は,C1-C8結合リフォーム,断片化,および異なるステレオ化学による炭素移動を含む複数の反応経路を可能にします.
さらに関連する動画
関連する概念動画
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.


