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相关概念视频

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
E2 Reaction: Stereochemistry and Regiochemistry02:43

E2 Reaction: Stereochemistry and Regiochemistry

12.0K
Elimination reactions of alkyl halides can yield one or more alkenes depending on the specific regiochemical and stereochemical considerations. While the regiochemistry of the reaction governs the location of the double bond in the product, the stereochemical requirements often influence the geometry.
When a substrate with two different β hydrogens undergoes an E2 elimination, the presence of a strong base can yield two regioisomeric alkenes. The more-substituted alkene is the major...
12.0K
E1 Reaction: Stereochemistry and Regiochemistry02:43

E1 Reaction: Stereochemistry and Regiochemistry

10.1K
One of the critical aspects of the E1 reaction mechanism, as also observed in E2, is the regiochemistry, with multiple regioisomers obtained as products. In the example discussed, the presence of water as a weak base favors elimination over substitution to generate two alkenes. Given that alkenes’ stability increases with the number of alkyl groups across the double bond, typically, E1 reactions lead to the Zaitsev product, for this is more substituted and stable than the Hofmann product.
10.1K
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
Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration02:34

Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration

8.7K
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.
8.7K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.5K
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.
2.5K

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[DPEPhosbcpCu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst
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光激发性合铜复合介导E →Z异构使运动分辨率成为可能

Hao Zhang1, Congcong Huang2, Xiang-Ai Yuan2

  • 1State Key Laboratory of Analytical Chemistry for Life Science, Jiangsu Key Laboratory of Advanced Organic Materials, Chemistry and Biomedicine Innovation Center (ChemBIC), School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.

Journal of the American Chemical Society
|June 8, 2022
PubMed
概括
此摘要是机器生成的。

这项研究引入了一种新型的光化学方法,用于对E-基体进行对Z-基体的选择性异构化. 这种催化方法提供了高效的运动分辨率,在热条件下是一个挑战.

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Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs
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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs
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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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科学领域:

  • 摄影化学
  • 不对称的催化
  • 有机合成

背景情况:

  • 不对称的合成对于制造富含的分子至关重要.
  • 赛马体的分离是一种常见的工业合成合物方法.
  • 催化酶选择性运动分辨率的E-到Z-异构体是具有挑战性的.

研究的目的:

  • 开发一种直接对E-素进行反选择性E → Z异构的方法.
  • 通过光化学手段实现2-styrylpyrrolidines的运动分辨率.
  • 探索激发性催化中的激发状态反应性.

主要方法:

  • 使用光刺激性铜复合物作为催化剂.
  • 研究了2- styrylpyrrolidines的对抗选择性E → Z异构.
  • 进行机械实验和密度函数理论 (DFT) 计算.

主要成果:

  • 通过光刺激性铜复合体实现了前所未有的反选择性E → Z异构.
  • 已经证明了2-styrylpyrrolidines的有效动态分辨率.
  • 作为分辨率的基础,确定了基质-催化剂复合物的差异化率.

结论:

  • 开发了一种新型的光化学转换,以实现反选择性运动分辨率.
  • 扩大了运动分辨率的范围,
  • 建立了激发状态的新反应模式.