Molecular electron density theory has been performed with the B3LYP/6-31(d,p) method to study the [3+2] cycloaddition processes between azidobenzene and propionaldehyde, the reactivity indices, activation and reaction energies are computed. The reaction and activation energies indicate that this [3+2] cycloaddition reaction is regiospecific, in good agreement with the experimental results. ELF examination revealed that the mechanism of these cycloaddition reactions takes place in two steps. In addition, a docking approach was performed on the products investigated, and the interaction with the protein protease COVID-19 (PDB ID: 6LU7), the results confirm that the presence of triazole and isoxazole rings increases the affinity of these products.