4 results on '"Díaz‐Oviedo, Christian David"'
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2. The Catalytic Asymmetric Intermolecular Prins Reaction
- Author
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Díaz-Oviedo, Christian David and Díaz-Oviedo, Christian David
- Abstract
The development of strategies for the transformation of olefins represents a highly rewarding challenge in chemical synthesis, due to the versatile reactivity and widespread accessibility of this functionality. The reactions of olefins with heteroatom-containing electrophiles result both in carbon–carbon bond formation and introduction of heteroatoms in the molecular skeleton, thus allowing to convert the relative structural simplicity of olefins into complex structures. The following work describes the catalytic, asymmetric, intermolecular reaction between aryl olefins and paraformaldehyde, known as the Prins reaction, enabled by the development of sterically-confined imino-imidodiphosphate (iIDP) Brønsted acid catalysts. By careful fine-tuning the catalyst structure, a great number of aryl olefins could be transformed, covering a broad range of electron density on the alkene moiety. In this way, enantiomerically-enriched 1,3-dioxanes were efficiently prepared from inexpensive and commercially available reagents. The obtained enantioenriched 1,3-dioxane rings could also be transformed to the corresponding optically-active 1,3-diols. These compounds constitute valued intermediates for the synthesis of multiple pharmaceutically-relevant molecules, such as Fluoxetine®, Dapoxetine® and Tomoxetine®, among others. Additionally, the developed catalytic, asymmetric Prins reaction was successfully utilized for the synthesis of several deuterium-containing enantioenriched 1,3-dioxanes, where the position and degree of deuteration could be controlled by proper choice of the starting materials. Mechanistic studies (isotope-labeling experiments and computations) showed that the reaction using the confined iIDP as catalyst proceeds by a highly asynchronous, concerted pathway, whereas a catalyst with a more open active site, such as p-toluenesulfonic acid, shifts the reaction to take place by a stepwise mechanism. Taken together, the work described in this thesis represents a new
- Published
- 2022
3. Estudio de la reacción entre β-(4-hidroxifenil) etilaminas y aldehídos no enolizables competencia entre las reacciones de Betti y de Pictet-Spengler
- Author
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Díaz Oviedo, Christian David and Quevedo Pastor, Ariel Rodolfo
- Subjects
54 Química y ciencias afines / Chemistry ,Supramolecular templates ,Betti reaction ,Aminación reductiva ,Plantillas supramoleculares ,Tyramine ,Tricomponent reaction ,Reacción de Eschweiler Clarke ,Reacción tricomponente ,66 Ingeniería química y Tecnologías relacionadas/ Chemical engineering ,Tiramina, bases de Schiff ,Reacción de Betti ,Schiff bases ,Reductive amination ,Aromatic mannich reaction ,Eschweiler clarke reaction ,Reacción tipo Mannich aromática - Abstract
La reacción entre β-(4-hidroxifenil)etilamina (tiramina) y aldehídos no enolizables (aromáticos, heteroaromáticos y α,β-insaturados) condujo a la formación de las respectivas bases de Schiff con rendimientos moderados, que se explican por la baja densidad electrónica en el átomo de nitrógeno de tiramina en comparación con fenetilamina, su análogo no hidroxilado, con la que se obtienen también bases de Schiff por reacción con aldehídos no enolizables con rendimientos mucho mayores. Las bases de Schiff derivadas de tiramina son débilmente electrofílicas, por lo que no reaccionaron con su parte fenólica ni con un fenol altamente activado (β-naftol). Se sintetizaron tiraminas N-sustituidas con grupos bencílicos (N-benciltiraminas) por medio de reacciones de aminación reductiva indirecta (reducción de las bases de Schiff con borohidruro de sodio). La reacción de Nbenciltiramina frente a 3-nitrobenzaldehído no condujo a ningún producto tipo base de Betti o de Pictet-Spengler y, solo al utilizar DMF como disolvente en condiciones drásticas (reflujo y catálisis ácida), se obtuvieron productos de transamidación con el disolvente y de posterior reducción por ácido fórmico generado in situ. La reacción tricomponente de Nbenciltiramina con 3-nitrobenzaldehído y β-naftol, a reflujo y con catálisis ácida, condujo a la base de Betti correspondiente con bajo rendimiento, indicando de nuevo la baja electrofilia de los iones iminio intermediarios. Por estudios computacionales se encontró que N-benciltiramina forma dímeros supramoleculares por puentes de hidrógeno en disolución, generando una plantilla para reacciones de macrociclación, lo que se comprobó en la reacción de N-benciltiraminas con formaldehído, donde se obtuvieron Nbencilazaciclofanos fenólicos. La presencia de sustituyentes electrodonores en el grupo Nbencilo favoreció la macrociclación aumentando la densidad electrónica en el átomo de nitrógeno, mientras que grupos electroatractores requirieron tiempos largos de reacción y la dirigieron hacia productos de condensación lineal N-metilados, por un mecanismo tipo Eschweiler-Clarke. Las plantillas supramoleculares de tiraminas primarias y secundarias dirigen la reacción de macrociclación, siempre que no haya un fenol más activado en el medio. Abstract. The reaction of β-(4-hydroxyphenyl)ethylamine (tyramine) with non-enolizable aldehydes (aromatic, heteroaromatic and α,β-unsaturated) led to the formation of the respective Schiff bases with moderate yields, which are due to the low electronic density on nitrogen atom of tyramine, in comparison to the one of phenethylamine, its non-hydroxylated analogue, with which Schiff bases are also obtained by reaction with non-enolizable aldehydes, although with much higher yields. Schiff bases from tyramine are weakly electrophilic, which serves as explanation for the fact that they did not react by nucleophilic addition, neither with their phenolic part nor with a highly activated phenol (β-naphthol). N-benzyl substituted tyramines (N-benzyltyramines) were synthesized by indirect reductive amination reactions (Schiff bases reduction with sodium borohydride). The reaction of N-benzyltyramine with 3-nitrobenzaldehyde did not lead to any product, either of Betti or Pictet-Spengler reactions and, only by using DMF as solvent in drastic conditions (reflux and acid catalysis), two products were obtained: a transamidation product with the solvent and its derivative from posterior reduction with formic acid, formed in situ. The tricomponent reaction of N-benzyltyramine, 3-nitrobenzaldehyde and β-naphthol, at reflux with acid catalysis, led to the respective Betti base with low yield, proving the low electrophilic character of the intermediate iminium ion. With the aid of computational calculations, it was found that N-benzyltyramine tends to form supramolecular dimers in solution, creating a template for macrocyclization reactions, which was proven in the reaction of N-benzyltyramines with formaldehyde, where phenolic N-benzylazacyclophanes were obtained. Electron-donating substituents on N-benzyl group favored macrocyclization by increasing electron density on nitrogen atom. Conversely, electron-withdrawing groups required long reaction times and led to linear N-methylated condensation products by an Eschweiler-Clarke mechanism. Supramolecular templates from primary and secondary tyramines lead the macrocyclization reaction, as long as there is no other activated phenol in reaction mixture. Maestría
- Published
- 2014
4. Chiral Phosphoric Acid Catalyzed Conversion of Epoxides into Thiiranes: Mechanism, Stereochemical Model, and New Catalyst Design.
- Author
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Duan M, Díaz-Oviedo CD, Zhou Y, Chen X, Yu P, List B, Houk KN, and Lan Y
- Abstract
Computations and experiments leading to new chiral phosphoric acids (CPAs) for epoxide thionations are reported. Density functional theory calculations reveal the mechanism and origin of the enantioselectivity of such CPA-catalyzed epoxide thionations. The calculated mechanistic information was used to design new efficient CPAs that were tested experimentally and found to be highly effective. Bulky ortho-substituents on the 3,3'-aryl groups of the CPA are important to restrict the position of the epoxide in the key transition states for the enantioselectivity-determining step. Larger para-substituents significantly improve the enantioselectivity of the reaction., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)
- Published
- 2022
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