エノンの直接C-Hα-アリレーションとArI (O2CR) 2の反応剤
Felipe Cesar Sousa E Silva1, Nguyen T Van1, Sarah E Wengryniuk1
1Department of Chemistry , Temple University , 1901 North 13th Street , Philadelphia , Pennsylvania 19122 , United States.
Journal of the American Chemical Society
|December 17, 2019
まとめ
この研究では,高価ヨウ素反応剤を用いたエノンの直接アルファアリレーションのための金属のない方法が導入されます. このアプローチは,価値ある有機化合物を合成するための伝統的なクロスカップリング方法よりも原子とステップ経済的な代替案を提供します.
科学分野:
- 有機化学
- 合成方法論
- カタリシス
背景:
- アルファ・ベータ不飽和ケトンのアルファアリレーションは重要な合成変換です.
- 従来の方法は,前機能化されたアルファヘロエノンのクロスカップリングに依存しており,それらはしばしば非効率であり,高価な触媒を必要とします.
- 直接のC−Hアリレーションは,より原子とステップ経済的なアプローチを提供するが,報告は限られている.
研究 の 目的:
- エノンの無金属直接C−Hアリレーションを開発する.
- 既存のアリレーション方法に対して,効率的で経済的な代替手段を提供すること.
- この新しい変容のメカニズムを探求するためです
主な方法:
- 超価ヨウ素反応剤を用いたエノンの非金属直接C-Hアリレーション.
- 反応は,局所生成のβ-ピリジニウムシリルエノールエーサーの還元性イオドニウムクライスン再配列による.
- アリルグループは,容易に入手可能なArI ((O2CCF3) 2) 反応剤から得られます.
主要な成果:
- 機能化された基板や移行金属触媒を必要とせずにエノンの成功アリレーション.
- この反応は,アリルとエノンの異なる置換パターンに対する耐性を示す.
- 組み込まれたアリルグループは,さらなる合成操作のためにヨウ素機能ハンドルを保持します.
結論:
- 開発された方法は,エノンのアルファアリレーションのための強力で持続的な経路を提供します.
- このメカニズムは,独特の還元性イオドニウムクライスン再配置と,アンポルの"エノニウム"中間物質を含んでいます.
- C−C結合形成を促進するベータピリジニウム分子の重要な役割が明らかにされた.
関連する概念動画
01:10α-Alkylation of Ketones via Enolate Ions
3.7K
Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by resonance, and its hybrid structure exhibits negative charges on the carbonyl oxygen and the α carbon. This ambident nucleophile can attack an electrophile via two possible sites: the carbonyl oxygen, known as O-attack, or the α carbon, known as C-attack. The nucleophilic attack via the carbanionic site is preferred. This is due to the...
3.7K
01:21Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
4.7K
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...
4.7K
01:27Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation
2.7K
Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, β-ketoesters, or β-diketones) and α,β-unsaturated carbonyl acceptors. Named after Sir Robert Robinson, who discovered it, this reaction yields a six-membered ring with three new C–C bonds (two σ bonds and one π bond).
2.7K
01:12Stereochemical Effects of Enolization
2.5K
The chiral α-carbon of the carbonyl compound is the stereocenter of the molecule. As shown in the figure below, when such a carbonyl compound undergoes racemization under an acidic or basic condition, an achiral enol is formed.
2.5K
01:26Synthesis of α-Substituted Carbonyl Compounds: The Stork Enamine Reaction
4.0K
α-Substituted ketones or aldehydes can be synthesized from enamines by the Stork enamine reaction, named after its pioneer Gilbert Stork. Enamines are useful synthetic intermediates where the lone pair on nitrogen is in conjugation with the C=C bond. They resemble enolate ions, as the resonance forms of both species have a nucleophilic α carbon.
4.0K
01:18Reactivity of Enols
3.9K
Enols are a class of compounds where a hydroxyl group is attached to a carbon–carbon double bond, which implies that it is a vinyl alcohol. A carbonyl compound with an α hydrogen undergoes keto–enol tautomerism and remains in equilibrium with its tautomer, the enol form. Usually, the keto tautomer is present in a higher concentration than the enol tautomer due to the higher bond energy of C=O compared to C=C. Moreover, the direction of the keto–enol equilibrium is...
3.9K