パラジウム触媒によるプロヌクレオフィルの非対称な添加がアレンに加わります
Barry M Trost1, Christoph Jäkel, Bernd Plietker
1Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA. bmtrost@stanford.edu
Journal of the American Chemical Society
|April 10, 2003
まとめ
この研究は,単純な添加を用いた,効率的なパラジウム触媒による非対称性アリルアルキレーションを導入しています. この方法は,優れたステレオ選択性を持つ複雑な炭素-炭素結合を作成するための高度な原子経済戦略を提供します.
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:
- 原子の経済は,効率的な化学合成に不可欠です.
- アレンの非対称アルキル化は,有機化学における重要な課題である.
- パラジウム触媒は,C-C結合形成のための多用途な経路を提供します.
研究 の 目的:
- 新しく,原子経済的に非対称なアリルアルキル化プロトコルを開発する.
- アレンの炭化水素化のためのパラジウム (((0) カタリシスを利用する.
- C-C結合形成において高い地域とステレオ選択性を達成する.
主な方法:
- パラジウム三酸塩二酸化物とキラルダイアミンリガンドから派生したパラジウム(0) 触媒を使用します.
- メルドラム酸とアズラクトンがアレンに添加されるのを触媒化する.
- 三酸またはアルファ-ブト酸化カリウムとヒップル酸を使用して反応条件を最適化します.
主要な成果:
- ベンジロキシアルケンの様々なメルドラム酸による非対称アリルアルキル化が成功し,高いエナチオセレクティブ性 (82-99% ee) が得られました.
- アズラクトンから異常な四次アミノ酸を効率的に合成し,優れたダイアステロ選択性 (13-20:1 dr) とエナチオ選択性 (85-94% ee) を有する.
- 非対称なC-C結合形成のための新しい地域選択的アプローチの実証.
結論:
- 新しく効率的なパラジウム触媒による非対称性アリルアルキレーションプロトコルが確立されました.
- この方法は,キラル分子を合成するための原子経済戦略を提供します.
- このプロトコルは,異なるプロヌクレオフィールと幅広い適用性を実証し,高いステレオコントロールを達成しています.
関連する概念動画
02:24Introduction to Electrophilic Addition Reactions of Alkenes
The double bond in a simple, unconjugated alkene is a region of high electron density that can act as a weak base or a nucleophile. The filled π orbital (HOMO) of the double bond can interact with the empty LUMO of an electrophile. A bonding interaction occurs when the electrophile attacks between the two carbons; the electrophile then accepts a pair of electrons from the π bond and undergoes addition across the double bond, yielding a single product.
Addition and elimination reactions can be...
Addition and elimination reactions can be...
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
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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...
02:35Regioselectivity 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.
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.
00:47Radical Formation: Addition
Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...
01:32Radical Anti-Markovnikov Addition to Alkenes: Thermodynamics
The anti-Markovnikov addition of hydrogen halides to an alkene is thermodynamically feasible only with HBr. The radical addition reaction with other hydrogen halides like HCl and HI is thermodynamically unfavorable.