関連する実験動画
Updated: Jun 24, 2026
06:26
Achieving Moderate Pressures in Sealed Vessels Using Dry Ice As a Solid CO2 Source
Published on: August 17, 2018
複合誘発的近接効果:カーバマート誘導型リチア反応に対する誘導群の方向性を変化させる効果
1Contribution from the Department of Chemistry, Roger Adams Laboratory, University of Illinois at Urbana-Champaign, 61801, USA.
Journal of the American Chemical Society
|July 18, 2001
まとめ
この研究では,アルファ-リチア化反応のためのバイサイクルカルバメットを調査しました. 形状的に制限されたカルバメータは,効率的なリチ化を促進し,特定の幾何学的な要因がプロセスを好む.
科学分野:
- 有機化学 オーガニック・ケミストリー
- ステレオセレクティブ合成
背景:
- 炭酸塩酸は,有機合成における多用途の機能群である.
- アルファ-リチア化は,カルバメトの機能化のための重要な反応である.
- カーバマート誘導リチエーションのステレオ化学的結果を理解することは極めて重要です.
研究 の 目的:
- 構造的および幾何学的要因がカルバマート誘導アルファリチ化に及ぼす影響を調査する.
- バイサイクルカルバマトのリチオン置換反応におけるステレオ化学的好みを決定する.
- 構成制限カルバメトとボックアミンの間のリチ化効率を比較する.
主な方法:
- 選択されたバイサイクルカルバメートの合成と調査.
- 立体選択的リチア・置換反応.
- リチア化の効率を評価するための競争実験.
- 移行状態をモデル化するための半経験的計算.
- コンフィギュレーションの安定性を評価するためのチン・リチウム交換実験.
主要な成果:
- オキサゾリジノン7-10は,立体選択的リチア置換による主要なシス-ダイアステロエーマー (cis-18-27およびcis-31-35) を生成した.
- 形状的に制限されたカルバメート (7,10,11,15) は,Bocアミン (4-6) に比べて,より高いリチエーション効率を示した.
- カーボニル酸素と標的陽子の間の小さな二面角と ~2.78 Å の C-H 距離は,カルバマート誘導のリチア化を好みます.
- 制約的幾何学は,カルバマート安定化オーガノリチウム種の構成の安定性を高めます.
結論:
- 構造的および幾何学的パラメータは,カルバマート誘導アルファリチ化の効率とステレオ選択性に大きく影響します.
- サイクルカルバメットは,制御されたステレオ選択的機能化のためのプラットフォームを提供します.
- この発見は,オルガノリチウム中間物質を含む合成戦略を設計するための貴重な洞察を提供します.
関連する概念動画
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...
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
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.
01:27Inductive Effects on Chemical Shift: Overview
The protons in unsubstituted alkanes are strongly shielded with chemical shifts below 1.8 ppm. Methine, methylene, and methyl protons appear at approximately 1.7, 1.2 and 0.7 ppm, while the proton signal from methane appears at 0.23 ppm. An electronegative substituent, such as chlorine, withdraws the electron density from the protons, increasing their chemical shift. Progressive substitution of the hydrogens in methane by chlorine shifts the proton signals increasingly downfield, to 3.05 ppm in...
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:18Directing and Steric Effects in Disubstituted Benzene Derivatives
When disubstituted benzenes undergo electrophilic substitution, the product distribution depends on the directing effect of both substituents. When the directing effects of both substituents reinforce each other, a single product is obtained. For example, bromination of p-nitrotoluene occurs ortho to the methyl group and meta to the nitro group, which is the same position, resulting in a single product. However, if the directing effects of the two groups oppose each other, the more strongly...