アルキルブロミドの脱水ハロゲン化のための軽度な,パラジウム触媒化された方法:合成と機械学的研究
Alex C Bissember1, Anna Levina, Gregory C Fu
1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Journal of the American Chemical Society
|August 22, 2012
まとめ
この研究では,β-ヒドリド除去をパラジアム触媒による脱水ハロゲン化に使用し,室温でのアルキルブロミドから端末オレフィンを効率的に生成します. この新しい方法は, (R) - メバロノラクトンの合成に成功裏に適用されました.
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
- 合成方法論 合成方法論
背景:
- パラジウムによって触媒化されたクロスカップリング反応は,有機合成において根本的な役割を果たします.
- ベータヒドリドの除去は,このようなプロセスにおいてしばしば望ましくない副作用となる.
- 末端オレフィン合成のための効率的な方法は,非常に求められています.
研究 の 目的:
- アルキルブロミドの脱水ハロゲン化のための新しいパラジウム触媒法を開発する.
- 典型的に望ましくないβ-ヒドリド除去ステップをキー変換として利用する.
- 公式の総合成でこの方法の有用性を実証し,そのメカニズムを解明する.
主な方法:
- パラジウム触媒によるアルキルブロミドの脱水ハロゲン化,フォスフィンリガンドを用いた.
- 開発された方法を (R) - メバロノラクトンの合成に適用する.
- 率決定のステップを決定し,重要な中間要素を特定するためのメカニズム調査.
主要な成果:
- この反応は,室温で優れた収量で進行する.
- この方法は,さまざまな機能群を許容します.
- 機械学的研究により,速度を決定するステップは基質に依存しており,L(2) PdHBrは中間物質ではないことが明らかになった.
結論:
- アルキルブロミドをパラジウム触媒で新しく効率的な脱ヒドロハロゲン化により,末端オレフィンに発展させました.
- この方法はオレフィン合成のための実用的な経路を提供し,正式な全合成によって検証されています.
- 機械学的洞察は,パラジウム触媒反応経路のより深い理解を提供します.
関連する概念動画
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In organic synthesis, the formation of products can be altered by changing the reaction conditions. For example, a dibromo addition product is formed when propene is treated with bromine at room temperature. In contrast, propene undergoes allylic substitution in non-polar solvents at high temperatures to give 3-bromopropene. In order to avoid the addition reaction, the bromine concentration must be kept as low as possible throughout the reaction. This can be achieved using N-bromosuccinimide...
Halogenation of Alkenes
Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
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Radical Anti-Markovnikov Addition to Alkenes: Mechanism
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The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy radical...
The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy radical...
Radical Anti-Markovnikov Addition to Alkenes: Overview
The addition of hydrogen bromide to alkenes in the presence of hydroperoxides or peroxides proceeds via an anti-Markovnikov pathway and yields alkyl bromides.
Formation of Halohydrin from Alkenes
An alkene, such as propene, reacts with bromine in the presence of water to yield a halohydrin. Halohydrins contain a halogen and a hydroxyl group attached to adjacent carbons. When the halogen is bromine, it is called a bromohydrin, while a chlorohydrin has chlorine as the halogen.
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Radical substitution reactions can be used to remove functional groups from molecules. The hydrogenolysis of alkyl halides is one such reaction, where the weak Sn–H bond in tributyltin hydride reacts with alkyl halides to form alkanes. Here, the reagent Bu3SnH yields tributyltin halide as a byproduct.
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