サイクロプロピレンイネスのニッケル触媒による再配置における選択性
1Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0850, USA.
Journal of the American Chemical Society
|April 21, 2005
まとめ
ニッケル/N-ヘテロサイクリックカルベン (NHC) 誘導反応は,サイクロプロピレン-イネスを再配置する. ItBuリガンドを使用すると,穏やかな条件下で選択的にサイクロペンタン製品を形成し,制御された合成経路を提供します.
科学分野:
- 有機金属化学 有機金属化学
- カタリシス カタリシス カタリシス
- 合成有機化学 合成有機化学について
背景:
- サイクロプロピレン-イネは,有機合成における多用途の基質である.
- ニッケル触媒反応は,分子変換のための効率的な経路を提供します.
- N-ヘテロサイクリックカルベン (NHCs) は,触媒における重要なリガンドである.
研究 の 目的:
- サイクロプロピレン-イネスのNi/NHC触媒による再配置を説明するために.
- 反応結果に対するNHCリガンドの影響を調査する.
- 特定のヘテロサイクリック製品の選択的合成を達成するために.
主な方法:
- ニッケル触媒. ニッケル触媒
- N-ヘテロサイクリックカルベン (NHC) リガンドスクリーニング,特にItBu.
- 軽度と選択性のために反応条件の最適化.
主要な成果:
- サイクロプロピレンイネスの再編成はNi/NHCシステムによって成功裏に触媒化されました.
- 製品として,サイクロペンタンおよびサイクロヘプテンベースの2種類のヘテロサイクルが観察されました.
- ItBu NHC リガンドを用いることで,サイクロペンタン製品が選択的に形成されました.
結論:
- Ni/NHC触媒システムは,サイクロプロピレン-イネの再編成に有効です.
- リガンドの選択,特にItBuは,製品の選択性を制御するために重要である.
- サイクロペンタン誘導体の軽度かつ選択的合成は達成可能である.
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...
02:36Regioselectivity 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.
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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
01:17Pericyclic Reactions: Introduction
Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...