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Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
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La hidroalcoxilación intermolecular anti-Markovnikov catalizada por el rodio de los acetilenos terminales se lleva a
Masataka Kondo1, Takuya Kochi, Fumitoshi Kakiuchi
1Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan.
Journal of the American Chemical Society
|December 15, 2010
Resumen
Este estudio introduce una nueva reacción catalizada por rodio para la creación de éteres enoles a partir de alquinas y alcoholes terminales. Este método libre de base logra altos rendimientos y Z-selectividad, ofreciendo una nueva ruta sintética.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- La catálisis de la catálisis.
- Metodología sintética de la metodología sintética.
Sus antecedentes:
- La hidroalcoxilación de los alquinos es una transformación crucial en la síntesis orgánica.
- Los métodos existentes a menudo requieren condiciones duras o grupos de dirección específicos.
- Desarrollar una hidroalcoxilación intermolecular eficiente y selectiva sigue siendo un desafío.
Objetivo del estudio:
- Desarrollar una nueva hidroalcoxilación intermolecular catalizada por metales de transición de las alquinas terminales.
- Para lograr la adición anti-Markovnikov de alcoholes a través del enlace triple alquino C-C.
- Para explorar la utilidad de los complejos inexplorados de 8-quinolinolato de rodio como catalizadores.
Principales métodos:
- Utilizando complejos de 8-quinolinolato de rodio como catalizadores.
- Reaccionan los alcinos terminales (arilo, alqueno y alquilacetileno) con los alcoholes alifáticos.
- Realizar la reacción en condiciones libres de bases.
Principales resultados:
- Logró la primera hidroalcoxilación intermolecular catalizada por metales de transición y anti-Markovnikov de alquinas terminales.
- Éteres de enol generados en altos rendimientos.
- Demostró una alta selectividad Z en la mayoría de los casos.
- Mostró la efectividad de catalizadores simples, pero poco utilizados, de 8-quinolinolato de rodio.
Conclusiones:
- La reacción catalizada por rodio desarrollada proporciona un método eficiente y selectivo para sintetizar éteres enoles.
- Este enfoque libre de bases amplía el alcance de la funcionalización de alquinos.
- Los complejos de 8-quinolinolato de rodio son catalizadores prometedores para transformaciones orgánicas difíciles.
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One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
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01:25Radical Anti-Markovnikov Addition to Alkenes: Overview
The addition of hydrogen bromide to alkenes in the presence of hydroperoxides or peroxides proceeds via an anti-Markovnikov pathway and yields alkyl bromides.
01:17Radical Anti-Markovnikov Addition to Alkenes: Mechanism
The reaction of hydrogen bromide with alkenes in the presence of hydroperoxides or peroxides proceeds via anti-Markovnikov addition. The radical chain reaction comprises initiation, propagation, and termination steps.
The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy radical...
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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.
02:35Regioselectivity 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.