Desenvolvimento de um novo protocolo sequencial três etapas para a síntese de 1,2,3-triazóis 1,4-dissubstituídos assistida por irradiação de micro-ondas

Abstract

Heterocyclic compounds has received a great attention in the branch of synthetic chemistry due to their wide field of applications, and among these, 1,2,3-triazoles are highlighted. In this work, a new three-step sequential protocol for the synthesis of 1,2,3-triazoles-1,4-disubstituted was developed using reactions under microwave irradiation. The reaction procedure aims at the combination of 3 sequential steps: a cross-coupling reaction of Sonogashira, followed by a deprotection reaction for formation of the terminal alkine and a 1,3-dipolar cycloaddition reaction catalyzed by copper (I) to obtain the 1,2,3-triazoles-1,4-disubstituted. The starting material used was 2-methyl-3-butin-2-ol, also known as MEBINOL, which has a much lower cost when compared to the analogue, trimethylsilacetylene. The deprotection stage represented an obstacle to be overcome in this reaction, considering that the reactivity of the substrates used proved to be extremely susceptible to the electronic nature of the substituents located in the aromatic ring. When electronic density removal groups were used, the 1,2,3-triazoles-1,4-dissubstituted were obtained with yields up to 74%. However, when electron donor groups were used, there was a significant reduction in yield. It is important to mention that for these cases the increase in the temperature of the reaction did not result in any increase in yields. The results which the development of a new three-step sequential procedure for the synthesis of 1,2,3-triazoles-1,4-disubstituted will be presented in detail. It should be noted that the sequential procedure directed at reducing the generation of residues from the purification of the intermediates, as well as at the possible loss of the terminal alkines generated in the deprotection stage, which in their majority are relatively volatile. Finally, it is important to mention that the use of microwave irradiation has reduced the reaction time involved in the three stages, contributing to increase the sustainability of the synthetic route.