Abstract: Addition reactions of SO2 to 1,3-butadiene and heteroderivatives were studied by performing density functional theory (DFT) calculations together with the 6311+G* basis set. Reactants, products, and transition states for each reaction were localized and the IRC connecting reactants and products was also obtained. Magnetic properties were evaluated along the reaction path to elucidate the characteristics of the reactions studied with respect to their aromaticity and pericyclic character. The addition can proceed by means of a cheletropic reaction giving a fivemembered cycle as a product or via a cycloaddition resulting on a sixmembered cycle. The results thus obtained indicate that for most reactions studied the energy barrier is smaller for the cycloaddition process, whereas the most stable product comes from cheletropic reaction. From the analysis of the magnetic properties along the reaction path, all reactions exhibit aromaticity enhancement near the transition state and, therefore, show pericyclic character.