Síntesis de alquenos mediante transposición de Claisen de éteres alil-vinílicos, parte II; vistas mecanicísticas; de la serie: El cuaderno de notas de química orgánica, un enfoque didáctico, N°10
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Rev. Bol. Quim
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Este es el décimo ensayo teórico en la serie: "El cuaderno de química orgánica, un enfoque didáctico". El objetivo de esta serie de estudios es ayudar a los estudiantes a disponer de una visión gráfica de reacciones de síntesis orgánicas de diversa naturaleza. Hemos tomado una serie de reacciones compiladas por W. Carruthers en: 'Some modern methods of organic synthesis', para las cuales hemos propuesto vistas mecanicísticas y didácticas. Este tema esta incluido en el capítulo "Formation of carbon-carbon double bonds" del mencionado texto. En el actual capítulo, abordamos un complemento de la transposición de Claisen de éteres alil-vinílicos. Un primer enfoque en este estudio comporta el sobresaliente hecho de la transposición de Claisen que guarda relación con el control estereoquímico que conduce a la definición de la posición de los sustituyentes en el nuevo enlace simple que se forma de la transposición. Este hecho remarcable sirve como una especie de transmisión de quiralidad a lo largo de la cadena carbonada. Hemos propuesto mecanismos para este hecho. Como un ejemplo hemos elaborado mecanismos para el paso clave en la síntesis de (+)-15(S)-prostaglandin A2 que involucra el mencionado control estereoquímico. También, hemos cubierto mecanicísticamente el tema de la geometría del doble enlace del enol eter y su control por medio del procedimiento descrito por Ireland. También hemos elaborado los mecanismos para la conversión de éster alílico en E-ceteno acetal o en Z-ceteno acetal y su subsecuente conversión en ácido incluyendo el ejemplo del propanoato de E-crotyl y de Z-crotyl.
This is the tenth theoretical assay in the series: "The Organic Chemistry Notebook Series, a Didactical Approach". The aim of this series of studies is to help students to have a graphical view of organic synthesis reactions of diverse nature. We have taken a series of reactions compiled by W. Carruthers in 'Some modern methods of organic synthesis', and we have proposed didactical and mechanistic views for them. This theme is included in the chapter "Formation of carbon-carbon double bonds" in the mentioned text. In the present chapter, we expose a complementing of Claisen rearrangements of ally-vinyl ethers. A first approach in this study comports the Claisen rearrangement feature regarding the stereochemical control that conducts to the definition of the positioning of substituents on the new single bond that arises from rearrangement. This feature serves as a sort of transmission of chirality along a carbon chain. We proposed mechanisms for this feature. As an example we elaborated mechanisms for a key step in the synthesis of (+)-15(S)-prostaglandin A2 involving the stereochemical control mentioned. We also covered from a mechanistic stand point the theme of the geometry of the enol ether double bond and its control by means of the procedure described by Ireland. We elaborated too, the mechanisms for the conversion of allylic ester into the E-ketene acetal or the Z-ketene acetal and subsequent acid formation including the example of the E-crotyl propanoate and the Z-crotyl propanoate.
This is the tenth theoretical assay in the series: "The Organic Chemistry Notebook Series, a Didactical Approach". The aim of this series of studies is to help students to have a graphical view of organic synthesis reactions of diverse nature. We have taken a series of reactions compiled by W. Carruthers in 'Some modern methods of organic synthesis', and we have proposed didactical and mechanistic views for them. This theme is included in the chapter "Formation of carbon-carbon double bonds" in the mentioned text. In the present chapter, we expose a complementing of Claisen rearrangements of ally-vinyl ethers. A first approach in this study comports the Claisen rearrangement feature regarding the stereochemical control that conducts to the definition of the positioning of substituents on the new single bond that arises from rearrangement. This feature serves as a sort of transmission of chirality along a carbon chain. We proposed mechanisms for this feature. As an example we elaborated mechanisms for a key step in the synthesis of (+)-15(S)-prostaglandin A2 involving the stereochemical control mentioned. We also covered from a mechanistic stand point the theme of the geometry of the enol ether double bond and its control by means of the procedure described by Ireland. We elaborated too, the mechanisms for the conversion of allylic ester into the E-ketene acetal or the Z-ketene acetal and subsequent acid formation including the example of the E-crotyl propanoate and the Z-crotyl propanoate.
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Vol. 33, No. 2