在氨基催化区域选择性 [4 + 2] 循环添加 β 置换循环和多重合马隆尼特里尔中的立体分离
Xin Feng1, Zhi Zhou, Rong Zhou
1Key Laboratory of Drug-Targeting and Drug Delivery System of the Ministry of Education, West China School of Pharmacy, West China Hospital, Sichuan University, Chengdu 610041, China.
Journal of the American Chemical Society
|November 16, 2012
概括
主要氨基酸催化循环乙烯的可切换反应. 根据基质,发生迈克尔添加或 [4 + 2] 循环添加,产生具有高选择性的复杂双循环结构.
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:
- 循环子是有机合成中的多功能构建块.
- 胺催化提供了一个强大的激活基质的策略.
- 控制反应途径和立体选择性仍然是一个关键的挑战.
研究的目的:
- 通过使用氨基基基因胺激活来研究β替代循环的可切换反应模式.
- 在复杂的分子架构的形成中实现高的二选择性和选择性.
- 阐明反应机制,区分协调和阶段性途径.
主要方法:
- 作为催化剂,利用来自天然素和素的原始氨基.
- 采用β替代的循环和不同的马洛尼替代物 (基,基,基尼和马洛尼).
- 研究了结相互作用在控制二聚体选择性的作用.
- 孤立的反应中间体来探测机械路径.
主要成果:
- 观测到γ-区域选择性维尼洛格斯迈克尔添加与基和尼.
- 实现了 [4 + 2] 循环添加与基或基基和基,形成双循环[2.2.2] 八度和类似结构.
- 已经证明了中等到优秀的二聚体选择性和反抗选择性.
- 通过采用多功能初级胺催化系统和特定添加剂 (酸) 实现了高 diastereodivergence.
- 识别了反应中间体,表明在协调的迪尔斯-阿尔德路径上有一个逐步的迈克尔-迈克尔级联机制.
结论:
- 通过二胺胺激活开发了一种可切换的循环子反应通路的催化系统.
- 成功合成了具有高立体控制的密度替代的bicyclo[2.2.2]octanes.
- 提供了机制性见解,表明观察到的 [4 + 2] 循环加法有逐步级联路径.
相关概念视频
[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.
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.
Diels–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.
Diels–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.
Regioselectivity of Electrophilic Additions-Peroxide Effect
In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.
Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.

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