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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.
01:26Thermal 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.
01:29Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
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
![[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.
01:28Diels–Alder Reaction Forming Cyclic Products: Stereochemistry
The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.
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イリジウム触媒によるエナンチオセレクティブポリエネサイクリング.
Michael A Schafroth1, David Sarlah, Simon Krautwald
1Eidgenössische Technische Hochschule Zürich, HCI H335, 8093 Zürich, Switzerland.
Journal of the American Chemical Society
|December 1, 2012
まとめ
新しい方法により,イリジウム触媒とルイス酸を用いたエナチオセレクティブポリサイクリングが可能になった. このアプローチは,単純なアルコールから高ステレオコントロールで多様なポリサイクル化合物を効率的に生成します.
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
- 合成方法論 合成方法論
背景:
- 多環化合物は,天然製品や医薬品における重要な構造モチーフです.
- 合成のための効率的でステレオ選択的な方法の開発は,有機化学における重要な課題です.
研究 の 目的:
- 複雑なカーボ・ヘテロポリサイクルリングシステムを構築するための新しい,高度にエナチオセレクティブな方法を開発する.
- 簡単に手に入る,分岐性ラセミアアリルアルコールを,出発材料として利用する.
主な方法:
- ルイス酸活性化と,イリジウム触媒によるアリリック置換の組み合わせを使用した.
- 枝分かれした,ラセミックなアリルアルコールを利用し,事前解決なしに直接使用することが可能になりました.
主要な成果:
- 独特の炭水化物およびヘテロポリサイクル化合物の多様な範囲を成功裏に合成しました.
- 高い収穫量と,製品の優れたエナチオ選択性 (≥99% ee) を達成しました.
- 開発されたポリサイクリング戦略の広範な適用性を実証しました.
結論:
![Solid-phase Synthesis of [4.4] Spirocyclic Oximes](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F58508.jpg&w=3840&q=75)
