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Thermal Electrocyclic Reactions: Stereochemistry01:17

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.
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

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.
Cycloaddition Reactions: Overview01:16

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.
Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

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.
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical 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

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関連する実験動画

Updated: Jun 14, 2026

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species
08:12

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species

Published on: August 16, 2018

エナチオセレクティブのチオウレア触媒化されたカチオンのポリサイクル化.

Robert R Knowles1, Song Lin, Eric N Jacobsen

  • 1Department of Chemistry & Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.

Journal of the American Chemical Society
|April 8, 2010
PubMed
まとめ

新しいチオウレア触媒は,ヒドロキシラクタムのエナチオセレクティブカチオン型ポリサイクリングを可能にします. 収量およびエナチオ選択性を含む触媒性能は,カチオン-ピ相互作用を促進する特定の芳香基によって最適化されます.

科学分野:

  • 有機化学 オーガニック・ケミストリー
  • カタリシス カタリシス カタリシス
  • ポリマーサイエンスの科学

背景:

  • エナチオセレクティブ合成は,医薬品と微細化学品にとって極めて重要です.
  • ハイドロキシラクタムのサイクリングは,複雑な分子構造への経路を提供します.
  • これらの変化のための効率的な触媒の開発は,依然として活発な研究分野です.

研究 の 目的:

  • ハイドロキシラクタムのエナチオセレクティブ・カチオン型ポリサイクリングのための新しいチオウレア触媒を報告する.
  • 反応結果に対する触媒構造の影響を調査する.
  • 観察されたエナチオセレクティビティの背後にあるメカニズムを解明する.

主な方法:

  • 新しいチオウレア触媒の枠組みの合成.
  • 開発された触媒を用いたエナチオセレクティブカチオン型ポリサイクリング反応.
  • 触媒の芳香代替剤の体系的な変化.
  • 反応産物の収量とエナティオメール過量 (ee) の分析.
  • 触媒と基板の相互作用を調査するためのメカニズム研究.

主要な成果:

  • ティオウレア触媒は,ヒドロキシラクタムのエナチオセレクティブカチオン性ポリサイクリングを成功裏に媒介した.

さらに関連する動画

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes
09:54

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes

Published on: September 12, 2018

Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
07:12

Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions

Published on: July 17, 2020

関連する実験動画

Last Updated: Jun 14, 2026

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species
08:12

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species

Published on: August 16, 2018

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes
09:54

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes

Published on: September 12, 2018

Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
07:12

Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions

Published on: July 17, 2020

  • 収量とエナチオセレクティビティの両方が,触媒の芳香的残留に非常に敏感でした.
  • 触媒のフレームワーク上の膨張性および偏極性領域は,最適な結果をもたらしました.
  • 証拠は,エナチオセレクティビティの鍵としてカチオン-ピ相互作用を含むメカニズムを支持しています.

    • 結論:

    • エナチオセレクティブ・ヒドロキシラクタムポリサイクリングのための新しいタイプのチオウレア触媒が開発されました.
    • 触媒の設計,特に芳香代替剤の性質は,エナチオセレクティビティを最適化するために重要です.
    • カチオン-ピ相互作用は,中介物質の安定化とステレオ化学的結果の指示において重要な役割を果たします.