3 research outputs found
Reacciones de CO2 con nucle贸filos carbonado y nitrogenados: aplicaciones en s铆ntesis
Las reacciones de carboxilaci贸n de nucle贸filos carbonados y nitrogenados, as铆 como de descarboxilaci贸n de los productos presentan una notable complejidad mecan铆stica que sigue siendo objeto de discusi贸n actualmente. El objetivo general del presente estudio plantea la exploraci贸n de estas reacciones y su eventual aplicaci贸n en s铆ntesis. En el primer cap铆tulo se describen las reacciones de carboxilaci贸n de aniones enolato y la qu铆mica de los 尾-cetocarboxilatos alcalinos correspondientes en el contexto de su aplicaci贸n en reacciones de alquilaci贸n monoselectiva. Los resultados muestran el impacto de la agregaci贸n y los equilibrios 谩cido-base sobre la evoluci贸n de los intermedios de reacci贸n, y c贸mo el control de estos factores permite llevar a cabo la monoalquilaci贸n selectiva de enolatos derivados de cetonas. El segundo cap铆tulo aborda la qu铆mica de carbamatos alcalinos en medio org谩nico y explora las posibilidades de aplicaci贸n como bases en s铆ntesis org谩nica. Los resultados ilustran c贸mo la concentraci贸n de CO2 en el medio de reacci贸n afecta a los equilibrios de transferencia de prot贸n y CO2 entre las especies implicadas. El cap铆tulo tercero estudia las reacciones de transferencia electr贸nica fotosensibilizada de aminas con CO2 y las v铆as de reacci贸n que tienen lugar en estos procesos. Los resultados proporcionan informaci贸n relevante para la comprensi贸n de las reacciones de carboxilaci贸n y descarboxilaci贸n de nucle贸filos carbonados y nitrogenados.Carboxylation reactions of carbon and nitrogen nucleophiles, as well as decarboxylation pathways of the corresponding products show significant mechanistic complexity which is still under discussion nowadays. The general aim of the present study addresses the exploration of these reactions and their eventual future synthesis application. The first chapter describes the carboxylation reactions of enolate anions and the chemistry of the corresponding alkaline 尾-ketocarboxylates in the context of selective monoalkylation reactions. The results show the impact of aggregation and acid-base equilibriums on the evolution of the reaction intermediates, and how to control these factors for achieving the selective monoalkylation of enolates derived from ketones. The second chapter addresses the chemistry of alkaline carbamates in organic solvents, exploring the application of these species as bases in organic synthesis. The results illustrate how CO2 pressure affects proton and CO2 transfer equilibriums between the species involved. Finally, the third chapter studies photoinduced electron transfer reactions of tertiary amines with CO2 and the reaction pathways occurring in these processes. The results provide relevant information for understanding the carboxylation-decarboxylation reactions of carbon and nitrogen nucleophiles
Photolysis of tertiary amines in the presence of CO2: the paths to formic acid, 伪-amino acids, and 1,2-diamines
The photolysis of triethylamine (1a) in the presence of carbon dioxide leads to the hydrogenation of CO2, the 伪-C-C coupling of triethylamine (1a), and the CO2-insertion into the 伪-C-H 蟽-bond of amine 1a. This reaction is proposed to proceed through the radical ion pair [R3N路+路CO2路-] generated by the photoionization of amine 1a and the electron capture by CO2. The presence of lithium tetrafluoroborate in the reaction medium promotes the efficient and stereoselective 伪-C-C coupling of 1a by enhancing the production of 伪-dialkylamino radicals and the isomerization of N,N,N',N'-tetraethylbutane-2,3-diamine (4a)
Reactivity of lithium 尾鈥慿etocarboxylates: the role of lithium salts
Lithium beta-ketocarboxylates 1(COOLi), prepared by the reaction of lithium enolates 2(Li+) with carbon dioxide, readily decarboxylate in THF solution unless in the presence of lithium salts, in which case they are indefinitely stable at room temperature in inert atmosphere. The availability of stable THF solutions of lithium beta-ketocarboxylates 1(COOLi) in the absence of carbon dioxide allowed reactions to take place with nitrogen bases and alkyl halides 3 to give alpha-alkyl ketones 1(R) after acidic hydrolysis. The sequence thus represents the use of carbon dioxide as a removable directing group for the selective monoalkylation of lithium enolates 2(Li+). The roles of lithium salts in preventing the decarboxylation and disproportionation reactions of lithium beta-ketocarboxylates 1(COOLi), and in determining the course of the reaction with bases and alkyl halides 3, are discussed