Reacciones catalíticas asimétricas de adición de 1,4- utilizando N-acilpirroles alfa, beta-insaturados como
Shigeki Matsunaga1, Tomofumi Kinoshita, Shigemitsu Okada
1Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Journal of the American Chemical Society
|June 17, 2004
Resumen
Los nuevos N-acilpirroles alfa, beta insaturados sirven como sustitutos de ésteres versátiles. Permiten una epoxidación asimétrica catalítica altamente eficiente y reacciones de Michael, produciendo valiosos compuestos quirales.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Catalización asimétrica por catálisis asimétrica.
Sus antecedentes:
- Se introducen los N-acilpirroles alfa, beta insaturados como nuevos reactivos.
- Los sustitutos de éster son cruciales en la química orgánica sintética.
Objetivo del estudio:
- Para sintetizar y explorar las aplicaciones de alfa, beta-insaturados N-acilpirroles.
- Desarrollar reacciones eficientes de epoxidación asimétrica catalítica y reacciones de Michael utilizando estos sustitutos.
Principales métodos:
- Reacción de Wittig para la síntesis de N-acilpirroles.
- catalizadores quirales a base de samario para la epoxidación asimétrica.
- catalizadores quirales basados en zinc para reacciones Michael asimétricas.
Principales resultados:
- Altos rendimientos y enantioselectividades (>99% ee) obtenidos en reacciones de epoxidación.
- Síntesis eficiente de una sola olla de epoxidos quirales a partir de aldehídos.
- Reacciones Michael asimétricas catalíticas exitosas de cetonas con altos rendimientos, diastereoselectividades y enantioselectividades.
Conclusiones:
- Los N-acilpirroles alfa, beta insaturados son reactivos efectivos y versátiles.
- Los métodos desarrollados ofrecen un acceso eficiente a valiosos bloques de construcción quirales.
- La unidad N-acilpirrol demuestra su utilidad para futuras transformaciones sintéticas.
Videos de Conceptos Relacionados
02:27Preparation of Alkynes: Alkylation Reaction
Introduction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
01:21Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
By replacing an α-hydrogen with a halogen, acid-catalyzed α-halogenation of aldehydes or ketones yields a monohalogenated product
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
01:09Conjugate Addition to α,β-Unsaturated Carbonyl Compounds
α,β-Unsaturated carbonyl compounds are molecules bearing a carbonyl and alkene functionality in conjugation with each other. The conjugation in the molecule leads to three resonance structures. The hybrid form exhibits two probable electrophilic sites: the carbonyl carbon and the β carbon.
01:17Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene
The electrophilic addition of hydrogen halides such as HBr to alkenes and nonconjugated dienes gives a single product as per Markovnikov’s rule.
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.
01:27Conjugate Addition (1,4-Addition) vs Direct Addition (1,2-Addition)
α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic attack via two modes: conjugate or 1,4-addition and direct or 1,2-addition.
Conjugate addition results in a thermodynamically stable product. The reaction retains the stronger C=O bond at the expense of the weaker C=C π bond. The process is slow as the β carbon is less electrophilic than the carbonyl carbon.
Direct addition products are formed faster owing to...
Conjugate addition results in a thermodynamically stable product. The reaction retains the stronger C=O bond at the expense of the weaker C=C π bond. The process is slow as the β carbon is less electrophilic than the carbonyl carbon.
Direct addition products are formed faster owing to...