聚烯的高反选择性质子启动的多环化
Karavadhi Surendra1, E J Corey
1Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Journal of the American Chemical Society
|July 12, 2012
概括
研究人员开发了一种高效的方法,可以从achiral前体中合成奇拉多环分子. 这种酶选择性质子启动的多环化提供了高产量和选择性,具有容易的催化剂回收.
科学领域:
- 有机化学 有机化学
- 不对称的合成方法
- 催化剂是一种催化剂.
背景情况:
- 状多环分子是天然产品和药品中重要的结构动图.
- 开发高效和选择性的合成方法仍然是有机化学的一个重大挑战.
- 阿希拉尔聚烯前体为构建复杂分子架构提供了多功能起点.
研究的目的:
- 开发一种用于合成奇拉多环分子的新型酶选择性方法.
- 为了研究使用的易斯酸催化剂进行质子启动的多环化.
- 在构建复杂的分子架构中实现高产量和选性.
主要方法:
- 合成三环到五环分子从Achiral聚烯前体.
- 使用反选择性质子启动的多环化.
- 使用1:1复合的o,o'-二-BINOL和五 (SbCl5) 作为性催化剂.
主要成果:
- 取得了优异的产量,每个形成的环约占90%.
- 获得了高的enantioselectivity,比例从20:1到50:1不等.
- 通过提取通过容易催化剂回收证明了该方法的实用性.
结论:
- 开发的方法提供了一种高效和高度对性多环分子的酶选择性途径.
- 使用o,o'-dichloro-BINOL/SbCl5复合体为不对称的多环化提供了一个实用的催化系统.
- 这种方法可以从简单的阿基拉基原材料中合成复杂的性结构.
相关概念视频
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.
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
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.
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
01:12Stereochemical Effects of Enolization
The chiral α-carbon of the carbonyl compound is the stereocenter of the molecule. As shown in the figure below, when such a carbonyl compound undergoes racemization under an acidic or basic condition, an achiral enol is formed.
02:35Regioselectivity 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.