通过可见光光催化剂通过非循环子的交叉分子间 [2+2] 循环添加
1Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53705, USA.
Journal of the American Chemical Society
|May 29, 2009
概括
可见光光催化使非循环的有效 [2+2] 异构化成为可能. 这种方法可以产生多样化的循环butan结构,具有高产量和立体选择性,即使使用阳光.
科学领域:
- 有机化学 有机化学
- 摄影化学的使用.
- 催化剂是一种催化剂.
背景情况:
- 环 [2+2] 循环添加物对于合成循环butan 结构至关重要.
- 对于这些反应,传统的紫外线光解方法往往效率低,选择性差.
- 开发选择性和高效的方法来形成不对称的循环butanes仍然是一个挑战.
研究的目的:
- 开发一种高效和有选择的方法,用于 [2+2] 不相似的非循环子的异构聚变.
- 探索可见光光催化剂在这种转化中的应用.
- 证明开发方法的可扩展性和广泛适用性.
主要方法:
- 在可见光照射下使用 (ruthenium) 的光催化剂.
- 采用不相似的非循环子作为反应伙伴.
- 调查反应条件,包括光源和尺度.
主要成果:
- 使用可见光和 (II) 光催化剂,实现了非循环的高效 [2+2] 异构化.
- 在良好的产量中获得了多样化的不对称的三和四替代循环butan结构.
- 在循环添加产品中表现出优异的 diastereoselectivities.
- 通过使用环境阳光在克尺度上展示了反应的效率.
结论:
- 可见光光催化为非循环 [2+2] 异构化提供了一种优越的替代UV光解.
- 开发的方法为复杂的循环butan衍生物提供了一种多功能和高效的途径.
- 使用易于获得的可见光源,包括阳光,提高了反应的实用性和可持续性.
相关概念视频
Cycloaddition Reactions: MO Requirements for Photochemical Activation
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
Cycloaddition Reactions: Overview
Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
Cycloaddition Reactions: MO Requirements for Thermal Activation
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
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
Selection Rules: Photochemical Activation
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.
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.
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.
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