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Una transformación de hidroaminación estereoselectiva para acceder a las indolizidinas polisubstituidas
Sergey V Pronin1, M Greg Tabor, Daniel J Jansen
1Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
Journal of the American Chemical Society
|January 24, 2012
Resumen
Un nuevo método de hidroaminación estereoselectiva permite la síntesis de alcaloides de indolizidina. Este proceso crea eficientemente cuatro estereocentros a partir de aminas insaturadas simples, produciendo compuestos naturales y no naturales.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química sintética de la química sintética.
- Química medicinal Química medicinal es el campo de la química medicinal.
Sus antecedentes:
- Los alcaloides de indolizidina son una clase significativa de productos naturales con diversas actividades biológicas.
- Las rutas sintéticas eficientes y estereoselectivas para estas moléculas complejas son muy buscadas.
Objetivo del estudio:
- Desarrollar un nuevo método estereoselectivo para la síntesis de alcaloides de indolizidina.
- Para establecer una reacción formal de hidroaminación aplicable a las dienaminas.
Principales métodos:
- El estudio informa una hidroaminación estereoselectiva, intramolecular y formal de las dienaminas.
- Esta reacción se produce a través de un mecanismo de hidroboración dirigida.
- El proceso establece efectivamente cuatro estereocentros en una sola transformación.
Principales resultados:
- El método desarrollado permite la construcción de arquitecturas moleculares complejas.
- Cuatro estereocentros son controlados con precisión durante la reacción.
- Se demuestra la síntesis de alcaloides de indolizidina tanto naturales como no naturales a partir de aminas insaturadas simples.
Conclusiones:
- Este trabajo presenta una poderosa nueva estrategia para acceder a los alcaloides de indolizidina.
- La hidroaminación mediada por hidroboración dirigida ofrece una ruta eficiente hacia andamios químicos valiosos.
- La metodología es prometedora para la síntesis de diversos derivados alcaloides para una mayor evaluación biológica.
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Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.
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.
01:22Preparation of 1° Amines: Azide Synthesis
Direct alkylation of ammonia produces polyalkylated amines, along with a quaternary ammonium salt. To exclusively prepare primary amines, the azide synthesis method can be used.
Azide ions act as good nucleophiles and react with unhindered alkyl halides to form alkyl azides. Alkyl azides do not participate in further nucleophilic substitution reactions, thereby eliminating the chances of polyalkylated products. Alkyl azides are reduced by hydride-based reducing agents, like lithium aluminum...
Azide ions act as good nucleophiles and react with unhindered alkyl halides to form alkyl azides. Alkyl azides do not participate in further nucleophilic substitution reactions, thereby eliminating the chances of polyalkylated products. Alkyl azides are reduced by hydride-based reducing agents, like lithium aluminum...
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Introduction
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02:23SN2 Reaction: Stereochemistry
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If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.