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Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule02:17

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If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
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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...
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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.
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Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is...
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Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
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The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
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La optimización bayesiana del punto de Utopía encuentra selectividad dependiente de la condición para la condensación

Derek M Dalton1, Richard C Walroth1, Caroline Rouget-Virbel2

  • 1Department of Synthetic Molecule Process Chemistry, Genentech, Inc., South San Francisco, California 94080, United States.

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|May 28, 2024
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Utopia Point Bayesian Optimization (UPBO) identificó las condiciones para la síntesis selectiva de N1 y N2-metilpirazol. Este método exploró eficientemente el espacio químico para la condensación de Knorr, revelando equilibrios intermedios clave.

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Área de la Ciencia:

  • Química orgánica
  • Química computacional

Sus antecedentes:

  • La condensación de pirazol Knorr es típicamente catalizada por el ácido.
  • El control de la regioselectividad en la síntesis de pirazol puede ser difícil.

Objetivo del estudio:

  • Identificar las condiciones de reacción para la formación altamente selectiva de isómeros de N1 y N2-metil-3-arilo.
  • Explorar un amplio espacio químico para optimizar la condensación de pirazol Knorr bajo condiciones básicas.

Principales métodos:

  • Se empleó la Optimización Bayesiana de Punto Utopía (UPBO) para navegar por vastos espacios de parámetros de reacción.
  • Se han investigado los equilibrios dependientes de la condición de los intermediarios de reacción.

Principales resultados:

  • UPBO identificó con éxito las condiciones para la síntesis selectiva de los isómeros N1 y N2.
  • Descubrió que la selectividad surge del equilibrio intermedio antes de la deshidratación.
  • Un intermediario hemiaminal formado de forma reversible fue clave para la vía del isómero N2.

Conclusiones:

  • UPBO permite una optimización eficiente de la conversión y la selectividad sin computación de alto rendimiento.
  • El estudio proporciona un nuevo enfoque para controlar la regioselectividad en la síntesis de pirazol.
  • La comprensión de los equilibrios intermedios es crucial para dirigir los resultados de la reacción.