キラルダイオキシランによるアルファ,ベータ不飽和エステルの高度なエナンチオセレクティブエポキシデーション
Xin-Yan Wu1, Xuegong She, Yian Shi
1Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA.
Journal of the American Chemical Society
|July 26, 2002
まとめ
この研究は,不飽和エステルのエナチオセレクティブエポキシデーションのための新しい触媒的方法を提示しています. フルクトーゼ由来ケトン触媒は,高いエナンチオセレクティブ性 (e.e.
科学分野:
- 有機化学 オーガニック・ケミストリー
- カタリシス カタリシス カタリシス
- アシンメトリック・シンセシス
背景:
- アルファ,ベータ不飽和エステルのエポキシデーションは,価値あるキラル構成要素の合成に不可欠です.
- 高度にエナチオセレクティブで効率的なエポキシデーション方法の開発は,有機合成における重要な課題です.
研究 の 目的:
- アルファ,ベータ不飽和エステルの新しい,高度にエナチオセレクティブなエポキシデーションを記述する.
- この変換における触媒としての果糖系ケトンの有用性を調査する.
- ディオキシランの形成とエポキシデーションの酸化剤としてのオクソンの有効性を実証する.
主な方法:
- エナチオセレクティブエポキシデーション反応のために,果糖由来ケトン (触媒2) を利用した.
- 有効なダイオキシラン種を生成する最終酸化剤としてオクソンを使用した.
- 一連のトランスおよび三置換アルファ,ベータ不飽和エステル基板をテストしました.
主要な成果:
- 様々な基質のエポキシデーションのために82%から98%の高エナチオセレクティビティ (ee's) を達成した.
- 電子欠乏オレフィンのエポキシデーションに in situ で生成されたダイオキシランを使用する可能性を実証した.
- 高いエナチオセレクティビティを促進する果糖系ケトンの触媒的役割が確認されました.
結論:
- 開発された方法は,エポキシド化されたアルファ,ベータ不飽和エステルへの高度なエナンチオセレクティブの経路を提供します.
- フルクトーゼ由来ケトン触媒は,電子欠乏オレフィンの非対称なエポキシド化に有効である.
- この研究は,ダイオキシラン化学を用いた触媒的非対称エポキシデーションの範囲を拡大します.
関連する概念動画
E2 Reaction: Kinetics and Mechanism
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E2 Reaction: Stereochemistry and Regiochemistry
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When a substrate with two different β hydrogens undergoes an E2 elimination, the presence of a strong base can yield two regioisomeric alkenes. The more-substituted alkene is the major product and...
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E1 Reaction: Stereochemistry and Regiochemistry
One of the critical aspects of the E1 reaction mechanism, as also observed in E2, is the regiochemistry, with multiple regioisomers obtained as products. In the example discussed, the presence of water as a weak base favors elimination over substitution to generate two alkenes. Given that alkenes’ stability increases with the number of alkyl groups across the double bond, typically, E1 reactions lead to the Zaitsev product, for this is more substituted and stable than the Hofmann product.
Acid-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...
Factors Affecting α-Alkylation of Ketones: Choice of Base
α-Alkylation of ketones is achieved in the presence of alkyl halides and a base. The reaction proceeds via the formation of an enolate ion followed by nucleophilic substitution. The choice of base employed is essential as it is the key factor in determining the reaction outcome.
The reaction involving bases like EtO− whose conjugate acid EtOH (pKa = 15.9) is stronger than the ketone (pKa = 19.2) results in an equilibrium mixture with higher ketone concentration. As a consequence, side reactions...
The reaction involving bases like EtO− whose conjugate acid EtOH (pKa = 15.9) is stronger than the ketone (pKa = 19.2) results in an equilibrium mixture with higher ketone concentration. As a consequence, side reactions...
Alkylation of β-Ketoester Enolates: Acetoacetic Ester Synthesis
Acetoacetic ester synthesis is a method to obtain ketones from alkyl halides and β-keto esters. The reaction occurs in the presence of an alkoxide base that abstracts the acidic proton of the β-keto esters. The step results in an enolate ion which is doubly stabilized. The enolate then reacts with an alkyl halide via the SN2 process to produce an alkylated ester intermediate with a new C–C bond. The hydrolysis of the intermediate, followed by acidification, results in an alkylated β-keto acid.


