化化和其他化化化化化碳-化合物键的化,使用化催化剂
Christos Douvris1, C M Nagaraja, Chun-Hsing Chen
1Department of Chemistry, Brandeis University, 415 South Street, Waltham, Massachusetts 02454, USA.
Journal of the American Chemical Society
|March 12, 2010
概括
新的催化剂使C-F,C-Cl和C-Br键的有效化能够使用试基. 这种反应选择性地准C(sp(3)) - 素键,除了CF(4) 之外,提供了广泛的基质范围.
科学领域:
- 有机金属化学 有机金属化学
- 催化剂是一种催化剂.
- 合成有机化学 合成有机化学
背景情况:
- 水解化是有机合成中至关重要的转化.
- 现有的方法往往缺乏选择性或需要苛刻的条件.
- 开发有效的催化剂,用于裂解强碳化合物键,特别是C-F键,仍然是一个挑战.
研究的目的:
- 开发用于各种碳-化合物键的化新型催化系统.
- 研究这些催化剂的范围和局限性,重点关注C-F,C-Cl和C-Br键裂变.
- 了解催化系统对不同基质的反应性和选择性.
主要方法:
- 使用试基酸盐等价物与化碳酸离子作为催化剂.
- 采用试基西兰作为水解化反应的固态测量试剂.
- 使用光谱和晶体学技术,包括X射线衍射,对催化系统和反应产品进行表征.
主要成果:
- 催化系统有效地促进C-F,C-Cl和C-Br键的化,仅在C ((sp ((3)) 混合的碳中.
- 广泛的含有C-F键的基质,包括基化物和基化物,会发生反应,而CF(4) 是不反应的.
- 分别通过各种基化物和初级基化物证明了化和化.
- 竞争性实验显示,在初级基化物中更轻的素具有动力偏好,但在C(6) F(5) CX(3) 系统中,化比化更快.
结论:
- 三基酸/化碳酸离子系统代表了有效和稳定的催化剂,用于化.
- 催化剂表现出独特的选择性,准C(sp(3)) -素键,并对各种素具有不同的反应性.
- 这种方法为合成化学家提供了一种有价值的新工具,特别是对于具有挑战性的基质的脱.
相关概念视频
Halogenation of Alkenes
Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
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Electrophilic Addition to Alkynes: Hydrohalogenation
Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.
Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene
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Base-Promoted α-Halogenation of Aldehydes and Ketones
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Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
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Radical substitution reactions can be used to remove functional groups from molecules. The hydrogenolysis of alkyl halides is one such reaction, where the weak Sn–H bond in tributyltin hydride reacts with alkyl halides to form alkanes. Here, the reagent Bu3SnH yields tributyltin halide as a byproduct.
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation reactions,...
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