3-ステリルピリジンの高度に地域選択性のある無酸素光循環化
F D Lewis1, R S Kalgutkar, J S Yang
1Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA. lewis@chem.northwestern.edu
Journal of the American Chemical Society
|July 18, 2001
まとめ
ステリルピリジンとアミノステリルピリジンの光化学反応により,アザフェナントレンが生成されます. 無酸素状態では,3-ステリルピリジンの誘導体は,安定したダイヒドロピリジンの中間体を通じて選択的に2‐アザフェナントレンを形成する.
科学分野:
- オーガニック・フォト化学
- ヘテロサイクル化学 ヘテロサイクル化学
- 反応メカニズム 反応メカニズム
背景:
- ステリルピリジンとアミノステリルピリジンは,重要なヘテロサイクルの化合物です.
- それらの光化学的変換を理解することは,合成アプリケーションにとって極めて重要です.
研究 の 目的:
- シスステリルピリジンとアミノステリルピリジンの光化学的振る舞いを調査する.
- アザフェナントレン形成の反応機構と地域選択性を解明する.
主な方法:
- 有酸素および無酸素条件下での光化学照射.
- 中間物質のスペクトル解析 (1H NMR,電子吸収)
- 実験スペクトルと計算スペクトルの比較.
主要な成果:
- 3-ステリルピリジンおよびその3'-アミノ誘導体から無酸素条件下で,2-アザフェナントレンの地域選択的形成.
- 酸素の存在下での混合2−および4−アザフェナントレン産物の形成.
- 1,7-水素のシフトによって形成された,中等に安定した1,4-ジヒドロピリジン中間物質の特定.
結論:
- 光循環の地域選択性は,リング開き,シグマトロピク再配置,酸素消火の速度によって影響を受けます.
- 提案されたメカニズムは,1,7-水素のシフトにより,二水素ピリジンの中間産物になり,その後,アザフェナントレン製品を形成します.
![[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F59739.jpg&w=3840&q=50)
![Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F60786.jpg&w=3840&q=50)
関連する概念動画
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.
02:36Regioselectivity 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.
01:17Thermal 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
01:13Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene
Bromination and chlorination of aromatic rings by electrophilic aromatic substitution reactions are easily achieved, but fluorination and iodination are difficult to achieve. Fluorine is so reactive that its reaction with benzene is difficult to control, resulting in poor yields of monofluoroaromatic products. To address this, Selectfluor reagent is used as a fluorine source in which a fluorine atom is bonded to a positively charged nitrogen.
01:14Photoluminescence: Applications
Photoluminescence offers a wide range of applications due to its inherent sensitivity and selectivity. This technique allows for both direct and indirect analyses of the analyte. Direct quantitative analysis is possible when the analyte exhibits a favorable quantum yield for fluorescence or phosphorescence. However, an indirect analysis may be feasible if the analyte is not fluorescent or phosphorescent, or if the quantum yield is unfavorable. Indirect methods include reacting the analyte with...