N-ハロスッキニミド/BF3-H2O,アロマティック剤の効率的な電離型ハロゲン化システム
G K Surya Prakash1, Thomas Mathew, Dushyanthi Hoole
1Donald P. and Katherine B. Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, California 90089-1661, USA. gprakash@usc.edu
Journal of the American Chemical Society
|December 2, 2004
まとめ
N-Halosuccinimides (NXS) は,BF(3)-H(2) Oにより効率的に活性化され,非活性化芳香化合物のハロゲン化を可能にする,費用対効果の高い試薬である. この新しい方法は,電友芳香置換反応の実用的なアプローチを提供します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- エレクトロフィリック・アロマティック・サブステーション
背景:
- N-Halosuccinimides (NXS) は,汎用性のあるハロゲン化剤である.
- NXSを活性化するには,通常,トリフッロメタン硫酸のような強い酸が必要です.
- 不活性化アロマティック化合物のハロゲン生成は,依然として合成上の課題である.
研究 の 目的:
- N-Halosuccinimidesを活性化するためのより経済的で効率的な方法を開発する.
- NXSを用いて無活性化された芳香基板のハロゲン化を可能にする.
- NXSの活性化とハロゲン化のメカニズムを調査する.
主な方法:
- N-Halosuccinimidesの活性化剤としてBF(3) -H(2) Oを使用しています.
- 不活性化された芳香化合物に対して電性ハロゲン化反応を行う.
- 密度関数理論 (DFT) の計算を用いて,反応機構と中間物質を研究する.
主要な成果:
- BF(3) -H(2) OはNXSを効率的に活性化させ,トリフローロメタン硫酸に匹敵しますが,より経済的です.
- NXS/BF(3)-H(2)Oシステムは,無効化された芳香基板をハロゲン化に成功しています.
- DFTの計算は,ハロゲン伝送を担当する超電性種の形成を明らかにしています.
結論:
- NXS/BF(3)-H(2) Oシステムは,電化ハロゲン化のための効率的で費用対効果の高い反応剤の組み合わせを表しています.
- この方法は,ハロゲン化非活性化アロマティックを合成するための貴重なツールを提供します.
- 機械的な経路を理解することで,将来のハロゲン化戦略の設計が向上します.
関連する概念動画
Formation of Halohydrin from Alkenes
An alkene, such as propene, reacts with bromine in the presence of water to yield a halohydrin. Halohydrins contain a halogen and a hydroxyl group attached to adjacent carbons. When the halogen is bromine, it is called a bromohydrin, while a chlorohydrin has chlorine as the halogen.
Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
Acid Halides to Carboxylic Acids: Hydrolysis
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
Acid Halides to Alcohols: LiAlH4 Reduction
Acid halides are reduced to alcohols in the presence of a strong reducing agent like lithium aluminum hydride.
The mechanism proceeds in three steps. First, the nucleophilic hydride ion attacks the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs as a leaving group, generating an aldehyde. A second nucleophilic attack by the hydride yields an alkoxide ion, which, upon protonation, gives a primary alcohol as...
The mechanism proceeds in three steps. First, the nucleophilic hydride ion attacks the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs as a leaving group, generating an aldehyde. A second nucleophilic attack by the hydride yields an alkoxide ion, which, upon protonation, gives a primary alcohol as...
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...
Radical Substitution: Allylic Bromination
In organic synthesis, the formation of products can be altered by changing the reaction conditions. For example, a dibromo addition product is formed when propene is treated with bromine at room temperature. In contrast, propene undergoes allylic substitution in non-polar solvents at high temperatures to give 3-bromopropene. In order to avoid the addition reaction, the bromine concentration must be kept as low as possible throughout the reaction. This can be achieved using N-bromosuccinimide...


