作为无处不在的功能,C-H键:一种通用方法,通过顺序的区域选择性C-arylation和N-alkylation,通过SEM组转换实现复杂的阿里化pyrazoles
Roman Goikhman1, Teresa L Jacques, Dalibor Sames
1Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
Journal of the American Chemical Society
|February 12, 2009
概括
这项研究引入了一种新型的催化C-H化方法,可用于pyrazoles,使复杂的triarylpyrazoles的区域选择性合成. 新的"SEM开关"策略允许精确控制药物应用中的替代剂放置.
科学领域:
- 有机化学 有机化学
- 合成方法论 合成方法论
- 药用化学 医学化学
背景情况:
- 皮拉是药品和蛋白质配体中至关重要的异环环.
- 现有的合成方法用于pyrazoles往往缺乏效率和区域控制.
- 对于创新的合成途径来获得各种pyrazole衍生物的持续需求.
研究的目的:
- 开发了第一个催化分子间C-H的pyrazoles的arylation.
- 建立一个区域选择性方法来合成复杂的酸.
- 为了创建一个通用的策略,以获得完全替代的pyrazoles与受控的regiochemistry.
主要方法:
- 催化性分子间C-H化,使用-皮瓦酸盐系统.
- 开发一个"SEM开关"用于区域选择性C-3结.
- 在C-5和C-3位置的顺序分离.
- 为区域选择性氨基替代剂引入N-化.
- 化和苏子基合用于C-4化.
主要成果:
- 确定了一种有效的-皮瓦拉酸催化系统,用于Pyrazole C-H arylation.
- 绘制了pyrazole C-H 键的反应性 (C-5>C-4>C-3).
- "SEM开关"在以前没有反应的C-3位置上实现了高效的arylation.
- 在完全的区域控制下实现了3,4,5-三烯醇的快速合成.
- 证明了SEM受保护的Pyrazoles的区域选择性N-化.
结论:
- 开发的催化C-H化,结合"SEM开关"和N-化,提供了一个快速和区域选择性的途径,以完全替代的pyrazoles.
- 这一策略提供了从简单的原始材料获取多样化的pyrazole支架.
- 该方法适用于受保护和自由的pyrazoles,增强其合成效用.
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相关概念视频
Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN1
Treating arylamines with nitrous acid gives aryldiazonium salts that are effective substrates in nucleophilic aromatic substitution reactions. The diazonio group in these salts can be easily displaced by different nucleophiles, yielding a wide variety of substituted benzenes. The leaving group departs as nitrogen gas, and this easy elimination is the driving force for the substitution reaction.
In the Sandmeyer reaction, for example, the diazonio group is replaced by a chloro, bromo, or cyano...
In the Sandmeyer reaction, for example, the diazonio group is replaced by a chloro, bromo, or cyano...
Nucleophilic Aromatic Substitution: Elimination–Addition
Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is confirmed through isotopic...
Diazonium Group Substitution: –OH and –H
Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.
Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions
Arenediazonium substitution reactions occur when the diazonium group is substituted by various functional groups such as halides, hydroxyl, nitrile, etc. For instance, arenediazonium salts react with copper(I) salts of chloride, bromide, or cyanide to form corresponding aryl chlorides, bromides, and nitriles. These reactions are named Sandmeyer reactions. Although the mechanism of this reaction is complicated, as illustrated in Figure 1, they are believed to progress via an aryl copper...
Five-Membered Heterocyclic Aromatic Compounds: Overview
Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom, respectively.
Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.


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