ニッケルO-およびC-エノラート複合体の合成とアルドール反応性
Juan Cámpora1, Celia M Maya, Pilar Palma
1Instituto de Investigaciones Químicas, Universidad de Sevilla, Consejo Superior de Investigaciones Científicas, Avda, Spain.
Journal of the American Chemical Society
|February 6, 2003
まとめ
サイクルニッケル複合体は容易なタウトメリゼーションを阻害し,異なる反応性研究を可能にします. O結合のタウトメアは,室温でアルデヒドと選択的に反応し,加法製品を形成する.
科学分野:
- 有機金属化学 有機金属化学
- 協調化化学について
- オーガニック・シンセシス オーガニック・シンセシス
背景:
- トランジションメタルエノラートは,通常,容易なC-/O-自動化を受けます.
- 個々のタウトマーの異なる反応性を研究することは,急速な相互変換のために困難です.
- サイクルリガンド構造は,金属複合体の安定性と反応性に影響を与える可能性があります.
研究 の 目的:
- 周期性ニッケルエノラートの個々のタウトマーの反応性を調査する.
- 阻害されたタウトメリゼーションプロセスの反応経路への影響を決定する.
- O結合ニッケルエノラートとアルデヒドの選択反応を調査する.
主な方法:
- サイクルニッケルエノラート複合物の合成 (1と2).
- 複合体のスペクトル学的および分析的特徴付け.
- 室温でのアルデヒドとの反応の研究.
主要な成果:
- 移行金属エノラートの容易なC-/O-タウトメリゼーションは,周期的なNi複合体1および2で著しく阻害されました.
- O結合タウトメア (2) は,室温でアルデヒドに対する選択的反応性を示した.
- アディション製品は,アルデヒドとO結合型タウトメアの反応から成功裏に形成されました.
結論:
- 循環構造は,タウトメリゼーションを効果的に抑制し,個々のエノラート形態の分離と研究を可能にします.
- O結合ニッケルエノラートは,特にアルデヒドのような電友との反応において,特定の反応性プロファイルを示します.
- この研究は,異なる金属エノラートタウトマーを使用した制御された合成アプリケーションの基礎を提供します.
関連する概念動画
01:21Acid-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...
01:09Conjugate Addition to α,β-Unsaturated Carbonyl Compounds
α,β-Unsaturated carbonyl compounds are molecules bearing a carbonyl and alkene functionality in conjugation with each other. The conjugation in the molecule leads to three resonance structures. The hybrid form exhibits two probable electrophilic sites: the carbonyl carbon and the β carbon.
01:10C–C Bond Formation: Aldol Condensation Overview
Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. The aldol condensation reaction presented in Figure 1 constitutes an aldol addition reaction followed by the dehydration process.
01:15Acid-Catalyzed Aldol Addition Reaction
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The acid-catalyzed aldol reaction is depicted in Figure 1.
00:57C–C Bond Cleavage: Retro-Aldol Reaction
The reverse of the aldol addition reaction is called the retro-aldol reaction. Here, the carbon–carbon bond in the aldol product is cleaved under acidic or basic conditions to form two molecules of carbonyl compounds. The mechanism of the reaction consists of three steps.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.
01:33Aldol Condensation vs Claisen Condensation
Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl compound. A base-promoted condensation between ester molecules to produce a ꞵ-ketoester is known as the Claisen condensation. In the presence of a base, both reactions involve deprotonation of the acidic α hydrogen to produce the corresponding enolates. The nucleophilic enolates attack their respective nonenolized carbonyl compound forming a tetrahedral intermediate.