相关概念视频
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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催化酶的反选择性聚环化.
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
概括
一种新方法使得使用化催化剂和易斯酸的酶选择性多环化成为可能. 这种方法有效地从简单的酒精中创建多种多环化合物,具有高立体控制.
科学领域:
- 有机化学 有机化学
- 催化剂是一种催化剂.
- 合成方法论 合成方法论
背景情况:
- 多环化合物是天然产品和药品中的重要结构动图.
- 开发高效和立体选择性的合成方法仍然是有机化学的一个重大挑战.
研究的目的:
- 开发一种新的,高度选择性的方法,用于构建复杂的碳和异聚环环系统.
- 为了利用随时可用的,分支的血性合醇作为起始材料.
主要方法:
- 采用了易斯酸激活和化催化替代的组合.
- 使用有分支的,血性合醇,允许直接使用而无需事先解决.
主要成果:
- 成功合成了多种独特的碳和异多环化合物.
- 产品获得了高产量和优异的反选择性 (≥99% ee).
- 证明了开发的多环化策略的广泛适用性.
结论:
- 开发的方法提供了一种强大而高效的途径,以获得聚合物丰富的多环结构.
- 这一策略为访问具有高立体化学保真度的复杂分子架构提供了有价值的工具.
![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)
