エナチオセレクティブオーガノ-SOMOサイクロアディション:オレフィンとアルデヒドから複合ピロリジンへの触媒的アプローチ
Nathan T Jui1, Jeffrey A O Garber, Fernanda Gadini Finelli
1Merck Center for Catalysis at Princeton University, Princeton, New Jersey 08544, USA.
Journal of the American Chemical Society
|July 7, 2012
まとめ
研究者らはアルデヒドとオレフィンのエナンチオセレクティブカップリングを用いてピロリジンを合成する新しい方法を開発した. この効率的なプロセスは,複雑な分子生成のための高いステレオ化学制御を提供します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 合成化学 合成化学とは
- カタリシス カタリシス カタリシス
背景:
- ピロリジンは,多くの医薬品や天然製品に含まれる重要なヘテロサイクリック化合物です.
- ピロリジンのための既存の合成方法は,長くまたはステレオ化学的制御が欠如する可能性があります.
研究 の 目的:
- 複雑なピロリジン誘導体を合成するための迅速でエナンチオセレクティブな方法を開発する.
- ラジカル・ポラー・クロスオーバー経路を含む反応メカニズムを解明する.
主な方法:
- アルデヒドと結合オレフィン間のSOMO活性化されたエナンチオセレクティブ (3 + 2) カップリング反応.
- 暫定的なエナミンラジカルカチオンと,その後の酸化段階を利用した.
- スタイレンとダイエンを含む様々なオレフィン の反応性を調査した.
主要な成果:
- ステレオ化学的に複雑なピロリジン製品の多様な範囲を成功裏に生成しました.
- 結合反応において,高い化学効率と優れたエナチオ制御を達成した.
- 変革のための急進的極性交差メカニズムを提案し,支持した.
結論:
- 開発された方法は,エナチオメリックに濃縮されたピロリジンへの簡単で効率的な経路を提供します.
- ラジカル・ポラー・クロスオーバー・メカニズムは,SOMOで活性化されたサイクロアディション反応に関する新しい洞察を提供します.
- このアプローチは,生物学的に関連するピロリジンを含む分子の合成に重要な可能性を秘めています.
関連する概念動画
Cycloaddition Reactions: Overview
Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
Cyclohexenones via Michael Addition and Aldol Condensation: The Robinson Annulation
Robinson annulation is a base-catalyzed reaction for the synthesis of 2-cyclohexenone derivatives from 1,3-dicarbonyl donors (such as cyclic diketones, β-ketoesters, or β-diketones) and α,β-unsaturated carbonyl acceptors. Named after Sir Robert Robinson, who discovered it, this reaction yields a six-membered ring with three new C–C bonds (two σ bonds and one π bond).
Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
Conjugate Addition to α,β-Unsaturated Carbonyl Compounds
α,β-Unsaturated carbonyl compounds are molecules bearing a carbonyl and alkene functionality in conjugation with each other. The conjugation in the molecule leads to three resonance structures. The hybrid form exhibits two probable electrophilic sites: the carbonyl carbon and the β carbon.
Regioselectivity 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.


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