スタウディンガー反応のトルコ選択性に関する新しい洞察
Yong Liang1, Lei Jiao, Shiwei Zhang
1Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
Journal of the American Chemical Society
|January 10, 2009
まとめ
スタウディンガー反応は,意外に,トルク・電子的に不利な産物を形成する. イミンの電子的性質は,製品比に影響を与え,スタウディンガー反応における単純なトルク電子的予測に挑戦する.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 反応メカニズム 反応メカニズム
- コンピューティング・ケミストリー
背景:
- スタウディンガー反応は,β-ラクトームを合成する重要な方法である.
- トルコ選択性のようなステレオ化学的結果を理解することは,合成制御に不可欠です.
- 以前のモデルは,非対称な反応物質との反応におけるステレオ選択性を完全に説明できませんでした.
研究 の 目的:
- スタウディンガー反応を制御するトルク選択性と電子効果を調査する.
- 製品の流通にインイン電子特性の影響を調査する.
- スタウディンガー反応におけるトルコエレクトロニック制御を他のサイクル反応と比較する.
主な方法:
- 非対称なサイクルケテンとサイクルイミンを用いたスタウディンガー反応の実験研究.
- 反応経路をモデル化するための密度関数理論 (DFT) 計算.
- ハメット分析は,電子効果と製品の比率を相関させるためのものです.
- 速度を決定するステップを決定するための運動競争の実験.
主要な成果:
- トルコ電子的に不利なドナー-インβ-ラクタムの形成が初めて観察されました.
- ハメット分析を通じて,電子的な性質とドナーアウト/ドナーインの製品比の間の明確な関係を確立しました.
- DFTと動的データは,ドナー入りとドナーアウトの経路の異なるレート決定ステップを明らかにしました.
結論:
- スタウディンガー反応におけるトルコエレクトロニック制御は,サイクロブテン環開き反応と著しく異なる.
- 非対称ケテンのスタウディンガー反応のダイアステロ選択性は,トルコエレクトロニックモデルによって単純に予測できない.
- イミンの電子効果は,スタウディンガー反応のステレオ化学的結果を導く上で重要な役割を果たします.
さらに関連する動画
関連する概念動画
02:23SN2 Reaction: Stereochemistry
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
01:34Woodward–Hoffmann Selection Rules and Microscopic Reversibility
Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
02:36Regioselectivity and Stereochemistry of Hydroboration
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.
02:35Regioselectivity of Electrophilic Additions-Peroxide Effect
In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.
01:26Limitations of Friedel–Crafts Reactions
Several restrictions limit the use of Friedel–Crafts reactions. First, the halogen in the alkyl halide must be attached to an sp3-hybridized carbon for the Friedel–Crafts reactions to occur. Vinyl or aryl halides do not react since the carbocations formed are unstable under the reaction conditions. Second, Friedel–Crafts alkylation is susceptible to carbocation rearrangement, and the major products obtained have a rearranged carbon skeleton. In contrast, the acylium ion is stabilized by...