4-ペンテン-1-オキシル基のサイクル化における6エンドの選択性について
Jens Hartung1, Rainer Kneuer, Christian Rummey
1Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany. hartung@chemie.uni-kl.de
Journal of the American Chemical Society
|September 24, 2004
まとめ
ラジカルサイクライゼーションに対する置換効果が研究されました. 置換剤の量を増やすことにより,6 - エンドトリグの選択性が強化され,FMOの好ましい相互作用と縮小したトルションストレスのためにテトラヒドロピランの形成を好む.
科学分野:
- 有機化学 オーガニック・ケミストリー
- コンピューティング・ケミストリー
- 反応メカニズム 反応メカニズム
背景:
- ラジカルサイクライゼーションは,有機合成における重要な反応である.
- 地域選択性の理解は,反応結果の制御に極めて重要です.
- 置換効果は,反応経路に大きな影響を与える可能性があります.
研究 の 目的:
- 4-置換された4-ペンテン-1-オキシルラジカルサイクライゼーションの地域選択性を調査する.
- 異なるリングサイズ (テトラヒドロフラン対テトラヒドロピラン) の形成を左右する要因を解明する.
- 実験的観測と計算による予測を相関させる.
主な方法:
- 密度関数理論 (DFT) を用いた実験調査と計算研究を組み合わせた.
- ペンテニル基の4位における置換剤の系統的変化.
- 移行状態のエネルギーと幾何学的パラメータの分析.
主要な成果:
- 6-エンドトリガー選択性の漸進的な増加は,置換剤のサイズ (H < CH3 < C(CH3) 3 < C6H5) が増加するにつれて観察されました.
- テトラヒドロフラン形成 (5-exo-trig) は,より小さな置換剤に好意的であった.
- テトラヒドロピラン形成 (6-エンドトリグ) は,テルトブチルおよびフェニル置換剤に好意的であった.
結論:
- 地域選択性は,トルションストレスの相互作用と境界分子軌道 (FMO) 相互作用のバランスによって支配されます.
- FMOの相互作用は,トランジション状態のエネルギーを低下させることで,大容量の置換物に対する6エンドトリガーサイクリングを好みます.
- 扭力ストレスは6内トリガー経路では作用するが,5外トリガー経路では作用しない.
関連する概念動画
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A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
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Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
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