A THEORETICAL ANALISYS OF THE REACTIVITY OF ACYL AZAHETEROCYCLES AS DIENOPHILES IN CYCLOADDITION REACTIONS

In this work, we realized a theoretical study of the behavior of N-tosylacylpyrroles and N-tosylacylindoles being electrophilic dienophiles in polar Diels-Alder reactions joint to different nucleophilic dienes: isoprene, 1-trimethylsiloxy-1,3-butadiene, and Danishefsky's diene. Calculations were developed considering the experimental results of these reactions in thermal conditions. The computational theorical methods employed are based in the Density Functional Theory. Electrophilicity and nucleophilicity indexes, based in the energy of frontier molecular orbitals HOMO and LUMO, were the parameter used to explore the feasibility of the cycloaddition. It was observed that the acyl pentaheterocycles suffer the cycloaddition yielding indol derivatives, and, the benzofused ones convert into carbazole derivatives. The regioselectivity was predicted using the Fukui function to achieve local electrophilicity and nucleophilicity indexes. Also, the reaction mechanisms of some selected cases were analyzed in order to understand the reaction path. Considering the mechanism study, a unique and notably asynchronous transition state was found between the reactants and the primary cycloadduct.  As a consequence of the theoretical study we can conclude that these reactions are concerted and asynchronous cycloadditions and that the sterochemistry is defined by the acyl group in the dienophile and the substituent groups of the dienes. Only the reactions where Danishefsky's diene participates are completely regioselective.