有机催化转移化循环乙
Jamison B Tuttle1, Stéphane G Ouellet, David W C MacMillan
1Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
Journal of the American Chemical Society
|September 28, 2006
概括
这项研究引入了第一个循环子的enantioselective有机催化转移化. 一种新的iminium催化策略有效地减少了使用廉价源的替代环基.
科学领域:
- 有机化学 有机化学
- 不对称的催化剂.
- 绿色化学 绿色化学
背景情况:
- 循环子是重要的合成中间体.
- 对合成性分子至关重要.
- 有机催化剂为非对称合成提供一种无金属的方法.
研究的目的:
- 开发了第一个对循环子进行enantioselective有机催化转移化.
- 建立一个新的iminium催化策略,用于不对称的减少.
- 从替代的α,β不和环基合成β-类固醇循环.
主要方法:
- 使用iminium催化剂与imidazolidinone 4作为不对称的催化剂.
- 采用三丁汉茨赫作为一种廉价的源.
- 将该方法应用于五,六和七个成员的循环子系统.
主要成果:
- 首次成功实现了循环乙的酶选择性有机催化转移化.
- 证明了催化剂4对各种循环子基质的广泛适用性.
- 产生的β-类固醇循环子具有高的enantioselectivity.
- 证实了不对称的感应感应与已建立的立体化学模型保持一致.
结论:
- 开发了一种新且高效的有机催化方法,用于对循环子进行enantioselective降解.
- 阴催化策略为获得性循环子提供了一种有价值的工具.
- 催化剂4显示了广泛的基质范围和可预测的立体化学结果.
相关概念视频
02:50Catalysis
The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
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.
01:17Thermal 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.
01:26Photochemical 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
01:17Pericyclic Reactions: Introduction
Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...
01:27Catalysis
Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...