サイクロペンタディエンのエンドダイメリゼーションにおける4+2および2+4サイクロードダクトにつながる予期せぬバイスペリサイクリック移行構造
Pierluigi Caramella1, Paolo Quadrelli, Lucio Toma
1Dipartimento di Chimica Organica, Università degli Studi di Pavia, Viale Taramelli, 10, I-27100 Pavia, Italy.
Journal of the American Chemical Society
|February 14, 2002
まとめ
サイクロペンタディエンの二酸化は,独特の移行状態を経て,ステレオ特異的にエンドプロダクトを形成します. この構造は,好ましいエンド経路にとって極めて重要な二次軌道相互作用を明らかにします.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 化学動力学 化学動力学
- コンピューティング・ケミストリー
背景:
- ディエルス・アルダー反応は,基本的な有機変異である.
- 反応機構,特にステレオ選択性を理解することは,有機合成の鍵です.
- サイクロペンタディエンの二酸化は,ダイエルス・アルダー反応の典型的な例です.
研究 の 目的:
- サイクロペンタディエンのエンドダイメリゼーションのステレオ特異的メカニズムを解明する.
- 移行状態の構造の性質を調査する.
- エンドオセレクティブ性を支配する電子的要因を特定する.
主な方法:
- 反応をモデル化するために,計算化学の方法が採用されました.
- 移行状態構造の分析が行われました.
- 二次軌道相互作用が調査されました.
主要な成果:
- ダイメリゼーションは,非同期的で対称なバイスペリサイクルの移行構造を通して進行します.
- この移行状態は,4+2と2+4サイクロアディション経路の両方を統合します.
- 魅力的なセーレム/ハウク二次軌道相互作用は,エンドアプローチの重要なファシリテーターとして特定されました.
結論:
- この研究は,サイクロペンタディエンの二分化のための新しい移行状態を明らかにしています.
- 二次軌道相互作用は,反応のステレオ特異性を指示する上で重要な役割を果たします.
- この発見は,ペリサイクル反応の基本原理についてより深い洞察をもたらします.
関連する概念動画
02:33Stereoisomerism of Cyclic Compounds
In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...
01:16Structure of Conjugated Dienes
Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
01:26Thermal 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.
01:17Thermal 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.
01:16Cycloaddition 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](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2Ffiles%2Fmedia%2Fscience-education%2Fscience-education-thumbs%2F12417.jpg&w=3840&q=75)
01:16[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.