DFT calculations were performed with Gaussian 09 program. The geometry of each species was optimized using the B3LYP functional and the 6-31+G(d,p) basis set. The DFT method with B3LYP functional has been proven to be a suitable method for the study of several cycloaddition reactions. Solvent effects (methanol) were evaluated through full optimizations using the SMD-continuum solvation method. Frequency calculations were performed at the same theoretical level as for geometry optimizations to determine the nature of the stationary points: the transition structures (TSs) had one imaginary frequency, and the reactants, the intermediate structures, and the products had no imaginary frequencies; and to obtain thermal free energy corrections. The intrinsic reaction coordinates (IRCs) were calculated to verify the connectivity of the TSs with the correct local minima. Single-point energies were computed at the B3LYP/6-311+G(d,p) level in methanol using the B3LYP/6-31+G(d,p) geometries. The reported free energies were calculated at 298.15 °K and 1 atm in methanol.