4-ペンチン-1-オール4'-ペンチン-1-オール4'-ペンチン-1-オール4'-ペンチン-1-オール4'-ペンチン-1-オール4'-ペンチン-1-オール4'-ペンチン-1-オール4'-ペンチン-1-オール4'-ペンチン-1-オール4
Yinghong Sheng1, Djamaladdin G Musaev, K Subba Reddy
1Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
Journal of the American Chemical Society
|April 11, 2002
まとめ
トングステンカルボニル触媒は,活性化バリアを下げることで,4-ペンチン-1-オールのエンドサイクロアイソメリゼーションを可能にします. この計算による研究は,これらの反応における観察された内分選択性を説明します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- コンピューティング・ケミストリー
- カタリシス カタリシス カタリシス
背景:
- サイクロアイソメリゼーション反応は,有機合成において極めて重要です.
- 反応機構と触媒の役割を理解することは,化学プロセスを最適化するために不可欠です.
研究 の 目的:
- 4-pentyn-1-ol.のエンドおよびエクソサイクロイソメリゼーションを計算的に調査する.
- これらの反応におけるボルンガムカルボニル触媒の役割を解明する.
- 実験的に観察された内分選択性を説明するために.
主な方法:
- 密度関数理論 (DFT) の計算.密度関数理論 (DFT) の計算.密度関数理論 (DFT) の計算.密度関数理論 (DFT) の計算.密度関数理論 (DFT) の計算.密度関数理論 (DFT) の計算.
- ダブルゼータとトリプルゼータベースのセットの使用.
- 触媒化されていない反応経路と,触媒化反応経路の比較.
主要な成果:
- 触媒化されていないサイクロアイソメリゼーションは,非常に高い活性化バリア (>50 kcal/mol) を表しています.
- トングステンペンタカーボニル触媒は,エンドサイクロアイソメリゼーションの速度決定バリアを26 kcal/molに大幅に低下させます.
- 触媒は,重要なヴィニリデンの中間物質を安定させ,ヒドリドの移動を促進します.
- エクソサイクロアイソメリゼーションは,触媒を使用しても高いバリア (47 kcal/mol) を保持しています.
結論:
- トングステンカルボニル触媒は,4-ペンチン-1-オールの効率的なエンドサイクロアイソメリゼーションに不可欠です.
- 触媒のメカニズムは,中間物質の安定化と,多段階のプロセスを促進することを含む.
- これらの発見は,関連反応における観察された内分選択性の理論的根拠を提供する.
さらに関連する動画
関連する概念動画
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
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.
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:34Woodward–Hoffmann Selection Rules and Microscopic Reversibility
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
![[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.