Novas alternativas catalíticas para a síntese de compostos heterocíclicos nitrogenados

Abstract

In this thesis, the results of three studies focused on the development of new catalytic alternatives in the synthesis of nitrogen-containing heterocyclic compounds are presented and discussed. New methodologies were explored that align the synthesis of high-value compounds with the principles of Green Chemistry, promoting more sustainable and clean approaches. In the first study, a methodology was developed for the in situ preparation of TBA(FeCl 3 Br), a complex formed by the reaction between FeCl 3 and tetrabutylammonium bromide (TBAB) under visible light irradiation. This photocatalytic complex enabled the selective oxidation of primary alcohols to aldehydes, that act as synthetic intermediates for the formation of the desired products. Using the developed method, nineteen benzochalcogenazoles (17 benzothiazoles and 2 benzoselenazoles) and fifteen quinazolinone derivatives were synthesized, with yields ranging from moderate to excellent. In the second study, ammonium niobium oxalate (ANO) was used as a cheap, low-toxicity, and highly efficient catalyst in the Paal-Knorr reaction for the synthesis of N-substituted pyrroles. The developed method allowed the synthesis of twenty-five molecules in up to 99% yield in a short reaction time and reuse tests demonstrated the good stability of the catalyst. The batch procedure was successfully adapted to a continuous flow system, allowing for 96% conversion of the starting materials into the desired pyrrole with a residence time of only 2 minutes (STY = 2.5 g/h -1 ). Additionally, it was developed a method that demonstrates the first application of ANO as a catalyst in multicomponent reactions for the synthesis of 3-nitroalkyl-Nsubstituted pyrroles. A total of twenty-five so far unprecedented molecules were prepared, with yields of up to 93%. The method also showed the possibility of reusing ANO. Furthermore, the reduction of the nitro group in one of the products to a primary amine proved to be feasible.