ベンザヌレーション反応のステレオ選択性:効率的な中央から軸のチラリティの移転
Andrei V Vorogushin1, William D Wulff, Hans-Jürgen Hansen
1Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
Journal of the American Chemical Society
|June 6, 2002
まとめ
研究者らは,フィッシャーカルベン複合体と1-pentyne.を用いてアロコルチキノイドを合成する際に,高いダイアステロ選択性を達成した. その他の反応では,適度な選択性が示され,熱力学的条件下で改善され,特定のアトロピソマーへの経路を提供しました.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 有機金属化学 有機金属化学
- 合成化学 合成化学とは
背景:
- フィッシャーカルベン複合体は,有機合成における多用途の反応剤である.
- ステレオ化学,特にダイアステレオ選択性およびアトロピソメリズムを制御することは,アロコルチキノイドのような複雑な分子を合成する上で極めて重要です.
研究 の 目的:
- アロコルチキノイド合成のためのフィッシャーカルベン複合体と1-ペンチンを含む反応のダイアステレオ選択性を調査する.
- ダイアステレオ選択性を高める方法,特に特定のアトロピソメアを得るための方法を探求する.
主な方法:
- フィッシャーカルベンの複合体 (4) が1-ペンチンと反応してアロコルチキノイド (5) が形成されます.
- 異なるフィッシャーカルベン複合体 (8) の類似反応により,製品 (9) が形成される.
- ダイアステレオ選択性に影響を与えるための熱力学的条件の適用.
主要な成果:
- 構成的に安定したアロコルチキノイドの製剤では,高いダイアステレオ選択性が達成された (5).
- 複合体 (8) の反応により,対極のアトロピゾーマーに対する中程度のダイアステレオ選択性を持つ製品 (9) が得られた.
- 熱力学的条件は,望ましいアトロピゾーマーに対するダイアステレオ選択性を著しく改善しました.
結論:
- フィッシャーカルベンの複合体は,高いダイアステロ選択性を持つアロコルチキノイドへの効果的な経路を提供します.
- ステレオ化学的結果は,熱力学的制御により,特定のアトロピソマーにアクセスするための戦略を提供することで,調節することができます.
さらに関連する動画
09:08Separation of Aldehydes and Reactive Ketones from Mixtures Using a Bisulfite Extraction Protocol
Published on: April 2, 2018
05:34Efficient Synthesis of Polyfunctionalized Benzenes in Water via Persulfate-promoted Benzannulation of α,β-Unsaturated Compounds and Alkynes
Published on: December 16, 2019
関連する概念動画
02:43E1 Reaction: Stereochemistry and Regiochemistry
One of the critical aspects of the E1 reaction mechanism, as also observed in E2, is the regiochemistry, with multiple regioisomers obtained as products. In the example discussed, the presence of water as a weak base favors elimination over substitution to generate two alkenes. Given that alkenes’ stability increases with the number of alkyl groups across the double bond, typically, E1 reactions lead to the Zaitsev product, for this is more substituted and stable than the Hofmann product.
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...
02:35Regioselectivity 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.
03:08Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
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.
01:18Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism
Birch reduction uses solvated electrons as reducing agents. The reaction converts benzene to 1,4-cyclohexadiene. The reaction proceeds by the transfer of a single electron to the ring to form a benzene radical anion. This anion is highly basic—it abstracts a proton from the alcohol to form a cyclohexadienyl radical. Another single electron transfer gives the cyclohexadienyl anion. A proton transfer from the alcohol forms 1,4-cyclohexadiene. Since this reduction occurs via radical anion...