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関連する概念動画

Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration02:34

Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration

The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[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.
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.
Cationic Chain-Growth Polymerization: Mechanism00:57

Cationic Chain-Growth Polymerization: Mechanism

The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the generated carbocation,...
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: May 28, 2026

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes
12:27

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

Published on: September 8, 2013

タクサジンを形成するカルボカチオンカスケード (carbocation cascade) が発生する.

Young J Hong1, Dean J Tantillo

  • 1Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, United States.

Journal of the American Chemical Society
|October 13, 2011
PubMed
まとめ

量子化学計算により,ゲラニルゲラニル二酸化物からタクサジネのバイオシンセシスの完全な経路が明らかになりました. このメカニズム的研究は,カルボケーションの中間形状を明確にし,タクサジネ合成酵素における基質アナログの非生産的結合指向を提案する.

科学分野:

  • バイオケミストリー バイオケミストリー
  • コンピューティング・ケミストリー
  • 有機化学 オーガニック・ケミストリー

背景:

  • タクサディエンは,抗がん剤パクリタキセルの前駆体である.
  • タクサディエンの生物合成には,複雑なカルボケーションの再編成が含まれています.
  • タクサディエン合成酵素に関する以前のメカニズム的提案は,限られた実験データに基づいていた.

研究 の 目的:

  • 量子化学計算を用いて,タクサディエン生物合成の完全な反応経路を解明する.
  • 理論的発見を既存の実験データと調和させ,ラベリング研究を含む.
  • タクサジネ合成酵素内の基板類型に対する拘束力のある指針を提案する.

主な方法:

  • 量子化学計算により,中間物質と移行状態の構造とエネルギーを決定しました.
  • 計算された経路は,ラベリング実験から得られた確立された実験結果と比較されました.
  • 理論的分析は,タクサジネ合成酵素のX線結晶構造データを解釈するために使用されました.

主要な成果:

  • ゲラニルゲラニルジフォスファートからタクサジエンへの完全な,エネルギー的に実現可能な経路が確立されました.
  • 計算された経路は実験的標識データと一致しているが,カルボケーション中間物質の新たな構成を示唆している.

さらに関連する動画

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

Published on: July 17, 2020

Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core
08:51

Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core

Published on: October 24, 2017

関連する実験動画

Last Updated: May 28, 2026

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes
12:27

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

Published on: September 8, 2013

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

Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core
08:51

Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core

Published on: October 24, 2017

  • 以前の機械的モデルと比較して,結合形成の同期性の微妙な違いが特定されました.
  • 理論的結果に基づいて,タクサジーン合成における2 - フッロロゲラニルゲラニル二酸化物の非生産的結合方向が提案されました.

    • 結論:

    • この研究は,タクサジンの生物合成のための詳細で理論的に検証されたメカニズムを提供します.
    • この発見は,テルペンサイクリングにおけるカルボケーション中間物質の構造的柔軟性に関する新しい洞察を提供します.
    • 提案された非生産的結合モードは,タクサジーン合成酵素基板相互作用の既存の解釈に挑戦しています.