CALCOGENÇÃO DE ARENOS ATIVADOS POR UMA ROTA SINTÉTICA MAIS VERDE

Abstract

In this work, a method for the functionalization of C(sp2)-H from activated arenes under heavy and transition metal-free conditions was developed. The most sustainable approach followed the Principles of Green Chemistry, following topics such as atomic economy, not using chlorinated solvents and formation of secondary products. The first stage of the project was to find ideal reaction conditions, using diphenyl diselenide and N,N dimethylaniline as standard substrates. Thus, the optimized reaction condition consisted of using 0.5 molar equivalent of PhICl2 as oxidizing agent, 1.4 Dioxane as solvent, at room temperature, in open atmosphere, for 30 minutes. Thus, N,N-Dimethyl-4-(phenylselenyl)aniline was arrived at in an isolated yield of 90%. Subsequently, a series of diorganoyl dichalcogenides (S, Se) were reacted with (hetero)arenes reaching a scope that revealed excellent results. The varied substituents having different electronic and steric effects tolerate the optimized reaction conditions well. In general, the conditions employed with diselenides indicated better yields when compared to disulfides. The influence of substituted groups on the participation in the formation of the C-Se and C-S connection was also notable, where donor groups demonstrated a better performance than withdrawers. The regioselectivity is seen from the greater coupling occurring in the –para position to anilines and phenols, and –ortho, when in the occurrence of substituents that weaken the ring resonance, or that present a steric effect. In order to demonstrate the effectiveness of the regioselective coupling, a gram-scale reaction was carried out where the proposed idea was validated, due to the good result found. As an outcome of the work, based on literature studies and control experiments, a mechanism was proposed, where there is the formation of the electrophilic species RYCl in situ, indicating an ionic pathway. Thus, it was possible to develop a greener effective synthetic route for the chalcogenation of C(sp2)-H.