Exploitation of the N-alkoxypyridinium photo-induced reactivity in organic chemistry

Cette thèse rapporte le développement de trois méthodologies photo-induites impliquant l’utilisation d’ions N-alcoxypyridinium.Tout d’abord, une nouvelle méthode de synthèse photocatalytique d’esters de phosphate a été développée. Celle-ci s’appuie sur la capacité des sels de N-alcoxypyridinium à pouvoir générer des radicaux oxygénés électrophiles très réactifs, via la photo-excitation d’un photocatalyseur permettant une réduction monoélectronique. Cette méthode a été appliquée à une large gamme de substrats. De plus des études mécanistiques poussées ont permis de proposer un mécanisme réactionnel plausible. Par la suite, une méthodologie de fonctionnalisation C–H d’hétéroarènes azotés, dérivée de la réaction de Minisci, a été détaillée. Cette réaction photo-induite n’utilisant pas de photocatalyseur a pu être étendue à la synthèse d’un large panel d’alcools hétéroaryles. De plus, cette méthodologie a permis de tolérer de nombreuses fonctions chimiques. Des études mécanistiques détaillées, impliquant des investigations expérimentales et théoriques, ont permis de révéler la présence d’une attaque nucléophile du carbonate sur le sel de pyridinium. L’intermédiaire formé s’est alors avéré être l’espèce photoactive de la réaction, permettant de générer le radical alcoxy. Pour finir, une méthodologie de synthèse d’aminopyridines a été envisagée à partir de sels de N-éthoxy-C-méthoxypyridinium, via la formation de sels de N-éthoxy-C-aminopyridinium par SNAr.This thesis reports the development of three photo-induced methodologies involving the use of N-akoxypyridinium ions.First, a new photocatalytic method for the synthesis of phosphate esters as been developed. This methodology is based on the ability of N-alkoxypyridiniums salts to generate highly reactive electrophilic oxygen-centered radicals through a monoelectronic reduction event by the excited state of the photocatalyst. This work has been applied to a wide range of substrates, and extensive mechanistic investigation allows the proposition of a reasonable mechanism. Next, a photo-induced Minisci-type C–H functionalisation of nitrogen heteroarenes was developed. This visible light photocatalyst free reaction was applied for the synthesis of a large panel of heteroaryl alcohols in good to excellent yields. Furthermore, the approach tolerates many functionalities. Detailed mechanistic studies combining experimental and theoretical investigations were conducted and reveled that a nucleophilic addition of carbonate to the N-alkoxypyridinium ion was occuring. This intermediate turned out to be the photoactive species in the reaction which is responsible for the generation of the alkoxy radical. Finally, a methodology for the synthesis of aminopyridines using N-ethoxy-C-methoxypyridinium salts was developed via the formation of N-ethoxy-C-methoxypyridinium salts by SNAr

Visible-Light-Mediated Access to Phosphate Esters

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Plastic scintillators with 1-phenyl-3-(mesityl)-2-pyrazoline as unique fluorophore for efficient neutron/gamma pulse shape discrimination

International audienceThe development of highly efficient plastic scintillators for neutron/gamma pulse shape discrimination is a matter of current interest. This is generally achieved using two fluorophores, with one of them being added to the polymer formulation at a concentration higher than typically 15 weight percent (wt%). Here, we report our results concerning the development of highly performant poly(vinyltoluene)-based (PVT) plastic scintillators for efficient fast neutron/gamma pulse shape discrimination, using 1-phenyl-3-(mesityl)-2-pyrazoline (1) as the only guest fluorophore. On our route during this study, the synthesis of the compound 1 has been revisited. Analysis and evaluation of the radioluminescence properties of these novel PVT-based plastic scintillators containing compound 1 are also described. In particular their light output and neutron/gamma discrimination ability were characterized. The sample doped with 15 wt% of compound 1 has a light output of 0.65 relative to EJ-200 and a neutron/gamma discrimination figure of merit of 0.84 in the range 450–500 keVee. •Efficient and inexpensive synthesis of 1-phenyl-3-(mesityl)-2-pyrazoline (PMP).•PMP as primary fluorophore of plastic scintillators for fast neutron/gamma PSD.•Polymer Characterization of highly doped PVT matrix with PMP