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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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関連する実験動画

Updated: May 30, 2025

[DPEPhosbcpCu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst
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銅依存ハロゲナーゼは,活性化されていないC-H結合の機能化を触媒とする.

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
まとめ
この要約は機械生成です。

新しい銅依存酵素であるApnUは,炭素-水素結合の新型ハロゲン化と偽ハロゲン化を可能にします. この発見は,C-H結合の機能化のための酵素学的能力を拡張し,二核銅酸化酵素の洞察を提供します.

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科学分野:

  • 生物化学
  • 酵素学
  • 有機化学

背景:

  • 炭素-水素 (C-H) 結合は有機分子にとって基本であり,化学合成の理想的な標的である.
  • C ((sp3) -H結合の選択的機能化は,合成化学における重要な課題である.
  • メタロ酵素は,酵素によるハロゲン化が限られているが,C ((sp3) -H結合の機能化のための強力なツールとして出現した.

研究 の 目的:

  • 活性化されていないC ((sp3) -H結合をハロゲン化および偽ハロゲン化できる新しい酵素を発見し,特徴づけること.
  • 酵素C ((sp3) -H結合の機能化の範囲を既存の制限を超えて拡大する.
  • 新しい酸化酵素の構造とメカニズムを明らかにする.

主な方法:

  • DUF3328タンパク質ファミリーのApnU酵素の発見と特徴付け.
  • 酵素活性と基質の範囲を決定する生化学的測定.
  • 電子パラマグネティック共振 (EPR) スペクトロスコーピーは,活性部位の銅センターを分析します.
  • 酵素のオリゴメール状態と二硫化結合を特定するためのプロテオミクス分析.

主要な成果:

  • ApnUの識別,繰り返しC ((sp3) -H塩化を行うことができる新しい銅依存ハロゲナーゼ.
  • ApnUの銅の活性部位を用いて前例のないC ((sp3) -Hヨデ化とチオシアン化を行う能力の実証.
  • ApnUの特徴は,本質的な二硫化結合を持つ共性結合のホモジマーである.
  • ApnUの双核型II銅活性部位をEPRスペクトルで決定する.

結論:

  • ApnUは,酵素C ((sp3) -Hハロゲナーゼの能力の有意な拡張を表しています.
  • 酵素の独特の二核銅活性部位は,新しいハロゲン化と擬似ハロゲン化反応を可能にします.
  • この研究は,二核銅依存酸化触媒としてのDUF3328ファミリー酵素の基礎的な理解を提供します.