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Acid-Catalyzed α-Halogenation of Aldehydes and Ketones01:21

Acid-Catalyzed α-Halogenation of Aldehydes and Ketones

3.6K
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...
3.6K
Halogenation of Alkenes02:46

Halogenation of Alkenes

15.3K
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.
15.3K
Base-Promoted α-Halogenation of Aldehydes and Ketones00:51

Base-Promoted α-Halogenation of Aldehydes and Ketones

3.4K
α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a base.  The reaction begins with the abstraction of  α hydrogen by the base to produce a nucleophilic enolate ion. This intermediate undergoes a subsequent nucleophilic substitution with the halogen to produce a monohalogenated carbonyl compound. If the starting substrate has more than one α hydrogen, it is difficult to stop the reaction...
3.4K
Reactions at the Benzylic Position: Halogenation01:11

Reactions at the Benzylic Position: Halogenation

2.4K
Benzylic halogenation takes place under conditions that favor radical reactions such as heat, light, or a free radical initiator like peroxide.
2.4K
Electrophilic Addition to Alkynes: Hydrohalogenation02:35

Electrophilic Addition to Alkynes: Hydrohalogenation

9.8K
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.
9.8K
Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride01:26

Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride

1.8K
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...
1.8K

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[DPEPhosbcpCu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst
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铜依赖酶催化未激活的C-H键功能化

Chen-Yu Chiang1, Masao Ohashi2, Jessie Le3

  • 1Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA, USA.

Nature
|January 29, 2025
PubMed
概括
此摘要是机器生成的。

一种新的依赖铜的酶,ApnU,使碳键的新型化和伪化成为可能. 这一发现扩大了C-H键功能化的酶能力,并提供了对双核铜氧化酶的见解.

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科学领域:

  • 生物化学
  • 酵素学
  • 有机化学

背景情况:

  • 碳- (C-H) 键是有机分子的基础,是化学合成的理想目标.
  • 在合成化学中,选择性功能化C ((sp3) -H键仍然是一个重大挑战.
  • 金属酶已经成为C(sp3) -H键功能化的强大工具,尽管酶化有限.

研究的目的:

  • 发现并描述能够化和伪化未激活的C ((sp3) -H键的新酶.
  • 扩大酶C(sp3) -H键功能化的范围,超出现有的限制.
  • 阐明一种新的氧化酶的结构和机制基础.

主要方法:

  • 来自DUF3328蛋白家族的ApnU酶的发现和表征.
  • 生物化学测试以确定酶活性和基质范围.
  • 电子磁共振 (EPR) 光谱分析活动部位的铜中心.
  • 蛋白质组学分析以确定酶的寡合状态和二硫化键链接.

主要成果:

  • 鉴定ApnU,一种新型的依赖铜的酶,能够进行代C ((sp3) -H化.
  • 使用其铜活性位进行前所未有的C ((sp3) -H化和硫酸化的能力.
  • 描述ApnU作为一种具有基本二硫化键的共价连接的同位素.
  • 通过EPR光谱测定ApnU中的双核II铜活性位点.

结论:

  • ApnU代表了酶C(sp3) -H酶能力的显著扩展.
  • 该酶独特的双核铜活性位使新的化和伪化反应成为可能.
  • 这项工作提供了对DUF3328家族酶作为双核铜依赖氧化催化剂的基础理解.