オクセタン基質カチオンの段階的なサイクロレバーションで,最初のC-O結合の割れ目が起こります
Miguel A Miranda1, M Angeles Izquierdo
1Departamento de Química/Instituto de Tecnología Química UPV- CSIC, Universidad Politécnica de Valencia, Camino Vera s/n, Apdo. 22012, 46022, Valencia, Spain. mmiranda@qim.upv.es
Journal of the American Chemical Society
|June 6, 2002
まとめ
2,4,6-トリアリル ((thia) ピリリウム塩はオクセタンサイクロレバーションを促進する. 2,3-ディフェニル-4-ヒドロキシメチロセタンの根幹カチオンはO-C2割れを経て,サブマイクロ秒でテトラヒドロフラン製品を形成します.
科学分野:
- フォトケミストリー フォトケミストリー
- 有機化学 オーガニック・ケミストリー
- 反応メカニズム 反応メカニズム
背景:
- 2,4,6-トリアリル ((thia) ピリリウム塩は,電子転送光敏感剤として確立されています.
- オキセタンリングシステムは,光化学的に誘発されたサイクル逆転に敏感です.
- 置換されたオクセタンの断片化の経路を理解することは,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:
- 光敏感化を用いて2,3-ディフェニル-4-ヒドロキシメチロセタンのサイクロレバーションメカニズムを調査する.
- 光化学反応に関与する中間種と断片化経路を解明する.
- 製品形成の運動学と競合する断片化の経路を決定する.
主な方法:
- 2,4,6-トリアリル ((thia) ピリリウム塩を光敏感剤として使用した.
- 2,3-ディフェニル-4-ヒドロキシメチロキセタン (1) の光化学を研究した.
- 反応中介物質と運動をモニタリングするために時間解像度スペクトロスコピーを使用しました.
主要な成果:
- オクセタン (1) の基質カチオンは,O-C2 結合分裂から始まり,段階的に割れていきます.
- 暫定的な中間物質は,酸素にスピンと炭素に電荷を局所する.
- 分子内核性攻撃により,2,3-ディフェニル-4-ヒドロキシテトラヒドロフーラン (4a) が微秒未満のスケールで形成されます.
- 競争的なC3-C4分裂により,トランススティルベン基のカチオン (λmax = 470 nm) が形成されます.
結論:
- オクセタン (1) の主要な光化学的経路は,連続的なO-C2分裂と分子内循環を伴う.
- 観測された動力学は,テトラヒドロフラン製品の急速な形成を示しています.
- この研究は,光感受性オキセタンサイクロリバーションに関する詳細なメカニズム的洞察を提供します.
関連する概念動画
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.
02:04Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
01:46Oxidative Cleavage of Alkenes: Ozonolysis
In ozonolysis, ozone is used to cleave a carbon–carbon double bond to form aldehydes and ketones, or carboxylic acids, depending on the work-up.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
03:00Preparation of Epoxides
Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
01:10C–C Bond Formation: Aldol Condensation Overview
Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. The aldol condensation reaction presented in Figure 1 constitutes an aldol addition reaction followed by the dehydration process.
00:57C–C Bond Cleavage: Retro-Aldol Reaction
The reverse of the aldol addition reaction is called the retro-aldol reaction. Here, the carbon–carbon bond in the aldol product is cleaved under acidic or basic conditions to form two molecules of carbonyl compounds. The mechanism of the reaction consists of three steps.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.