エナチオセレクティブで,アルキネスの脱対称化ブロモラクトニゼーション
Michael Wilking1, Christian Mück-Lichtenfeld, Constantin G Daniliuc
1Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster , Corrensstrasse 40, 48149 Münster, Germany.
Journal of the American Chemical Society
|May 18, 2013
まとめ
この研究では,脱対称化戦略を用いてアルキンの非対称的なブロモラクトニゼーションが実証されました. 容易に入手できる触媒とN-ブロモスクシニミド (NBS) は,高いエナチオ選択性を持つ貴重なブロモエノールラクトンの構成要素を効率的に生成します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- アシンメトリック・シンセシス
- カタリシス カタリシス カタリシス
背景:
- アルキンの機能化は,有機合成において極めて重要です.
- 複雑な分子を作るためのエナチオセレクティブ・メソッドの開発は,重要な課題です.
- ブロモエノール・ラクトンは,汎用性の高い合成中間物質です.
研究 の 目的:
- アルキンの非対称的なブロモラクトニゼーションを開発するために.
- エナチオセレクティブサイクライゼーションのデシンメトリゼーションアプローチを活用する.
- 価値あるブロモエノール・ラクトンの構成要素を生成する.
主な方法:
- アルキーンサイクライゼーションの脱対称化戦略を用いること.
- 商業的に利用可能な触媒 (DHQD) 2PHAL.を使用しています.
- N-ブロモスクシニミド (NBS) を安価なブロミン源として使用する.
主要な成果:
- ブロモエノール・ラクトンの高収量が得られる.
- サイクル化製品における高いエナチオセレクティブ性を得ました.
- テトラ置換アルケンと四次性ステレオセンターを含む合成製品.
結論:
- アルキンの非対称的なブロモラクトニゼーションは,非対称化によって実現可能である.
- (DHQD) 2PHAL触媒とNBSは,効率的な方法を提供する.
- その結果生成されるブロモエノール・ラクトンは,さらなる合成変換のための貴重な前駆体である.
関連する概念動画
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
02:47Alkynes 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.
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.
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
01:25Radical 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.
01:10α-Alkylation of Ketones via Enolate Ions
Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by resonance, and its hybrid structure exhibits negative charges on the carbonyl oxygen and the α carbon. This ambident nucleophile can attack an electrophile via two possible sites: the carbonyl oxygen, known as O-attack, or the α carbon, known as C-attack. The nucleophilic attack via the carbanionic site is preferred. This is due to the strong interaction...