乙烯基cyclopropanes和pi系统的 [5 + 2] 循环添加反应的不对称催化
Paul A Wender1, Lars O Haustedt, Jaehong Lim
1Department of Chemistry, Stanford University, Stanford, California 94305, USA. wenderp@stanford.edu
Journal of the American Chemical Society
|May 11, 2006
概括
研究人员为金属催化 [5 + 2] 循环添加物开发了高度选择性的催化剂. 这些催化剂有效地将乙烯基cyclopropanes (VCPs) 和pi系统转化为复杂的分子,具有高反体过剩.
科学领域:
- 有机化学 有机化学
- 催化剂是一种催化剂.
- 不对称的合成方法
背景情况:
- 金属催化循环添加对有机合成至关重要.
- (I) 复合物在催化 [5 + 2] 乙烯基cyclopropanes (VCPs) 和pi系统的循环添加物方面表现有前途.
- 之前的研究表明,在温和条件下运行的Rh (I) 催化剂.
研究的目的:
- 为了对催化 [5 + 2] 循环添加的性催化剂进行比较评估.
- 为了评估一种首选的催化剂[((R) -BINAP) Rh]+SbF6-的性能,使用各种基板.
- 开发一种反应选择性的预测模型.
主要方法:
- 选多个性催化剂.
- 测试优化的催化剂与多种类型的乙烯基cyclopropane和pi系统基板.
- 使用奇拉色谱 (chiral chromatography) 分析等离子体过量 (ee).
- 开发一种用于选择性预测的计算模型.
主要成果:
- 为了 [5 + 2] 循环添加,评估了几种性催化剂.
- 首选的催化剂,[((R) -BINAP) Rh]+SbF6 - - 在多种基质组合中实现了高反选择性 (>95% ee).
- 基质替代和带类型显著影响了选择性.
- 成功开发了一种选择性的预测模型.
结论:
- 化催化剂,特别是[((R) -BINAP) Rh]+SbF6-,使高度反选择性 [5 + 2] 循环添加成为可能.
- 开发的预测模型有助于理解和控制反应结果.
- 这项工作推进了非对称金属催化循环添加的领域.
相关概念视频
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.
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
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.
[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.
Pericyclic 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...
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.


