高度に地域選択性のある触媒的酸化結合反応:合成的および機械的調査
Kami L Hull1, Erica L Lanni, Melanie S Sanford
1Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, MI 48109, USA.
Journal of the American Chemical Society
|October 26, 2006
まとめ
パラジウム触媒による新しい方法は,室温でアリルピリジンの誘導体の効率的な酸化結合を可能にします. この反応は,様々な機能群と互換性があり,新しい二重C-H活性化メカニズムを介して進行します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- カタリシス カタリシス カタリシス
- 有機金属化学 有機金属化学
背景:
- パラジウムによって触媒化されたクロスカップリング反応は,有機合成において根本的な役割を果たします.
- 効率的で地域特有のC-H活性化戦略の開発は,依然として重要な課題です.
- アリルピリジン誘導体は,医薬品や材料における重要な構造モチーフである.
研究 の 目的:
- アリルピリジン誘導体の酸化結合のための新しい高効率のPd触媒法について報告する.
- 様々な機能群との反応の互換性と,その地域選択性を実証する.
- 前例のない触媒メカニズムを解明するために.
主な方法:
- 酸化結合反応のためにパラジウム触媒を使用した.
- 温度と基板の範囲を含む,調査された反応条件.
- C-H活性化ステップを含む反応経路を理解するために,メカニズム研究を行った.
主要な成果:
- アリルピリジン誘導体の高効率で地域選択的な酸化結合が達成されました.
- 室温での反応の成功が実証され,実用性を高めました.
- アリルハリドやチオフェンなどの様々な機能との互換性が確認されています.
- Pd (II) とPd (IV) センターでの二重ピリジン誘導のC-H活性化を含む新しいメカニズムを特定しました.
結論:
- 開発されたPd-触媒化された方法は,アリルピリジンの誘導体合成における重要な進歩を提供します.
- 前例のない二重C-H活性化メカニズムは,パラジウム触媒に対する新しい洞察を提供します.
- この方法論は,複雑な有機分子を合成する可能性を秘めています.
関連する概念動画
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.
02:44Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
01:22Heterogeneous Catalysis
Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...
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.
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
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.