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Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.1K
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.
2.1K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.4K
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.
2.4K
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction01:16

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

10.3K
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.
10.3K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

1.9K
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
1.9K
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

3.4K
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
3.4K
Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

7.9K
Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
7.9K

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Updated: Aug 4, 2025

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
09:45

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Published on: March 20, 2017

10.5K

リチウム媒介メカノケミカルサイクロデヒドロゲネーション

Kanna Fujishiro1, Yuta Morinaka2, Yohei Ono2

  • 1Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan.

Journal of the American Chemical Society
|April 3, 2023
PubMed
まとめ
この要約は機械生成です。

研究者らは,リチウム ((0)) を媒介する新しいメカノケミカルアニオンサイクロデヒドロゲネーションを開発した. このユーザフレンドリーな方法は,最も長い非置換分子ライレンであるクイントリレンを含む多環芳香炭化水素とナノグラフェンを効率的に合成します.

さらに関連する動画

A Protocol for Safe Lithiation Reactions Using Organolithium Reagents
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A Protocol for Safe Lithiation Reactions Using Organolithium Reagents

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Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes
12:07

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Published on: April 1, 2013

17.2K

関連する実験動画

Last Updated: Aug 4, 2025

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
09:45

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

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A Protocol for Safe Lithiation Reactions Using Organolithium Reagents
09:45

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Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes
12:07

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Published on: April 1, 2013

17.2K

科学分野:

  • 有機合成
  • 材料化学
  • ナノテクノロジー

背景:

  • サイクロデヒドロゲネーションは,ポリサイクル芳香炭化水素 (PAH),ヘテロアロマティック化合物,およびナノグラフェンの合成に不可欠です.
  • カリウムを使用したアニオン性サイクロデヒドロゲネーションはリレン構造を作るのに有効ですが,実用性,熱性,およびスケーラビリティが悪いです.
  • 既存の方法は,合成の広範な適用に重大な課題を提示しています.

研究 の 目的:

  • アニオンサイクロデヒドロゲネーションのための新しい,実用的でスケーラブルな方法を開発する.
  • PAHとナノゲンを合成するためのユーザフレンドリーなプロトコルを作成する.
  • 最長の非置換分子ライレンを含む 新種のナノゲンを合成する.

主な方法:

  • リチウム ((0) 媒介の機械化学アニオンサイクル脱水反応の開発.
  • 室温と空気中の通常のリチウム電線を使用します.
  • 計算式およびNMR分析による反応の範囲,メカニズム,およびグラムスケール合成の調査.

主要な成果:

  • 1,1-ビナフチルから効率的な合成を30分で94%の収量で達成した.
  • 反応の実用性,空気耐久性,室温での動作を証明した.
  • クインテルリレン ([5]リレン) を含む複数のサイクロデヒドロゲン化による新種のナノゲン合成に成功した.

結論:

  • リチウムを媒介する機械化学プロトコルは,既存の方法よりも実用性と適用性において重要な利点を提供します.
  • このユーザフレンドリーなアプローチにより 複雑なナノゲンの合成が可能になり 合成能力が拡大されます
  • この研究は,反応の範囲,メカニズム,および限界の包括的な理解を提供し,将来の応用への道を開きます.