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催化不对称的皮克特-斯潘格勒反应
Jayasree Seayad1, Abdul Majeed Seayad, Benjamin List
1Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany.
Journal of the American Chemical Society
|January 26, 2006
概括
一种新的催化不对称的Pictet-Spengler反应是使用奇拉酸开发出来的. 这种方法有效地从胺和化物中产生具有高产率和方位纯度的四-β-卡博林衍生物.
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:
- 皮克特-斯格勒反应是合成印类类化合物的关键方法.
- 开发不对称的变体对于获取质纯化合物至关重要.
研究的目的:
- 开发一种新的催化不对称的皮克特-斯格勒反应.
- 为了在四-β-carbolines的合成中获得高产量和酶选择性.
主要方法:
- 使用替代的胺和化物作为基质.
- 采用一种催化剂的酸作为催化剂.
- 优化反应条件以获得产量和反体过量.
主要成果:
- 成功合成了各种四-β-卡博林衍生物.
- 产品获得了高产量和优异的反体过剩 (ee).
- 证明了该反应与阿利法性和芳香性化物的广泛应用.
结论:
- 开发的催化不对称的皮克特-斯勒反应是一种高效的方法.
- 化酸催化提供了一个强大的工具,用于enantioselective合成.
- 这种方法提供了一条有价值的途径,以获得性四-β-卡博林支架.
相关概念视频
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
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.
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
01:34Woodward–Hoffmann Selection Rules and Microscopic Reversibility
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...