スカンジウムとイトリウムアルキル複合体による芳香性N-ヘテロサイクルの環開き反応
Colin T Carver1, Paula L Diaconescu
1Department of Chemistry & Biochemistry, University of California, Los Angeles, California 90095, USA.
Journal of the American Chemical Society
|May 22, 2008
まとめ
スカンジウムとイトリウム複合体は,芳香的N-ヘテロサイクルにおけるC-C結合を促進する. この反応は,シグマ結合のみを含む,拡張された二重結合結合を持つユニークなリング開かれたイミダゾール構造を形成します.
科学分野:
- 有機金属化学 有機金属化学
- ヘテロサイクル化学 ヘテロサイクル化学
- カタリシス カタリシス カタリシス
背景:
- アロマティックなN-ヘテロサイクルの強い炭素-窒素 (C-N) 結合の割れには,通常,金属元素の多重結合が必要です.
- C-N結合の活性化およびその後のC-C結合のための新しい触媒方法の開発は,合成化学にとって極めて重要です.
研究 の 目的:
- スカンジウムおよびイトリウムベンジル複合体によって媒介される芳香的N-ヘテロサイクルのC-C結合を調査する.
- この新しい結合反応のメカニズムと構造的結果を解明する.
主な方法:
- フェロセーン 1,1'-ダイアミドリガンドを含むスカンジウムおよびイトリウムベンジル複合体の合成.
- 1-メチリミダゾールと金属複合体の反応により,C-C結合が誘発される.
- 反応産物および中間物質を特徴付けるためのスペクトロスコピーおよび分析技術.
主要な成果:
- 金属複合体によって媒介された2つの1-メチリミダゾール分子のC-C結合が成功しました.
- リングが開いたイミダゾールと1-メチリミダゾール断片の結合によるイミダゾールの形成.
- シグマ結合の関与を示唆する二重結合の拡張結合を持つ製品の特徴.
結論:
- スカンジウムとイトリウム複合体は,芳香的N-ヘテロサイクルのC-C結合を効果的に媒介することができます.
- 観測された変換は,金属元素の多重結合ではなく,シグマ結合の再配置を含んでいる.
- この研究は,N-ヘテロサイクルの機能化のための有機金属触媒の範囲を拡大します.
関連する概念動画
01:14Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN1
Treating arylamines with nitrous acid gives aryldiazonium salts that are effective substrates in nucleophilic aromatic substitution reactions. The diazonio group in these salts can be easily displaced by different nucleophiles, yielding a wide variety of substituted benzenes. The leaving group departs as nitrogen gas, and this easy elimination is the driving force for the substitution reaction.
In the Sandmeyer reaction, for example, the diazonio group is replaced by a chloro, bromo, or cyano...
In the Sandmeyer reaction, for example, the diazonio group is replaced by a chloro, bromo, or cyano...
01:22Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction
The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.
01:20Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions
Arenediazonium substitution reactions occur when the diazonium group is substituted by various functional groups such as halides, hydroxyl, nitrile, etc. For instance, arenediazonium salts react with copper(I) salts of chloride, bromide, or cyanide to form corresponding aryl chlorides, bromides, and nitriles. These reactions are named Sandmeyer reactions. Although the mechanism of this reaction is complicated, as illustrated in Figure 1, they are believed to progress via an aryl copper...
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
01:11Nucleophilic Aromatic Substitution: Elimination–Addition
Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is confirmed through isotopic...
01:11ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...