ケテンのエステルの触媒的非対称合成
Sheryl L Wiskur1, Gregory C Fu
1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Journal of the American Chemical Society
|April 28, 2005
まとめ
新しいブロンステッド酸触媒法により,ケテンのエステルの多用途な非対称合成が可能になる. このアプローチは,有価なエナチオ濃縮アルコールと炭酸酸を生成し,有機合成を促進します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- アシンメトリック・シンセシス
背景:
- ケテンからエステル合成のための核フィルの触媒化された方法が存在します.
- これらの方法には,多用途性と有効性の限界があります.
研究 の 目的:
- 非対称エステル合成のためのより汎用的で効果的な方法を開発する.
- この変換のために,ブロンステッド酸触媒を使用します.
主な方法:
- ブロンステッドの酸塩化学の原理に基づいています.
- ヌクレオフィールによって触媒化されたプロセスを,ブロンステッド酸によって触媒化されたプロセスに変換する.
- ケテンのエステルの非対称合成.
主要な成果:
- ケテンから非対称的なエステル合成のための非常に汎用的で効果的なブロンステッド酸触媒プロセスが確立されました.
- 製品アリルエステルは,高いエナチオ選択性で合成されました.
- これらのアリルエステルは,エナンチオ濃縮アルコールとカルボキシル酸に成功裏に変換されました.
結論:
- 開発されたブレンステッド酸触媒法では,以前のヌクレオフィール触媒法よりも大きな利点があります.
- この方法は,価値あるキラル構造ブロックへの強力な経路を提供します.
- この戦略は,非対称合成の範囲と効率を高めています.
関連する概念動画
02:42Acidity of 1-Alkynes
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
01:01Acid Halides to Carboxylic Acids: Hydrolysis
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
01:28Amides to Carboxylic Acids: Hydrolysis
Amides can undergo either acid-catalyzed hydrolysis or base-promoted hydrolysis through a typical nucleophilic acyl substitution. Each hydrolysis requires severe conditions.
Acid-catalyzed hydrolysis:
Hydrolysis of amides under acidic conditions yields carboxylic acids. Since the reaction occurs slowly, hydrolysis requires the conditions of heat.
The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst. The protonation makes the amide carbonyl carbon more...
Acid-catalyzed hydrolysis:
Hydrolysis of amides under acidic conditions yields carboxylic acids. Since the reaction occurs slowly, hydrolysis requires the conditions of heat.
The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst. The protonation makes the amide carbonyl carbon more...
01:15Acid-Catalyzed Aldol Addition Reaction
The aldol reaction of a ketone under acidic conditions successfully forms an unsaturated carbonyl as the final product instead of an aldol. The acid-catalyzed aldol reaction is depicted in Figure 1.
01:10Factors Affecting α-Alkylation of Ketones: Choice of Base
α-Alkylation of ketones is achieved in the presence of alkyl halides and a base. The reaction proceeds via the formation of an enolate ion followed by nucleophilic substitution. The choice of base employed is essential as it is the key factor in determining the reaction outcome.
The reaction involving bases like EtO− whose conjugate acid EtOH (pKa = 15.9) is stronger than the ketone (pKa = 19.2) results in an equilibrium mixture with higher ketone concentration. As a consequence, side reactions...
The reaction involving bases like EtO− whose conjugate acid EtOH (pKa = 15.9) is stronger than the ketone (pKa = 19.2) results in an equilibrium mixture with higher ketone concentration. As a consequence, side reactions...
01:29Amino Acid Biosynthetic Pathways
Amino acid biosynthesis is essential for cell growth, protein synthesis, and metabolic regulation. Cells generate essential and non-essential amino acids from metabolic intermediates to sustain vital biological functions. These intermediates originate from key metabolic pathways: glycolysis, the tricarboxylic acid (TCA) cycle, and the pentose phosphate pathway. Important precursors include α-ketoglutarate, pyruvate, oxaloacetate, phosphoenolpyruvate, and erythrose-4-phosphate, which provide...