The mechanism of [2+2] cycloaddition reaction of cyclohexenone and its derivatives with vinyl acetate was studied at the B3LYP-D3/6-311++G(d,p) level of theory. Computations showed that this reaction occurs via a stepwise mechanism. The geometries of the first and second transition states were determined. Moreover, we investigated the effect of the chalcogens of the ketone function of the cyclohexenone on the cycloaddition reactions. The activation energies decrease significantly on proceeding from oxygen (O), through sulfur (S) and onto selenium (Se). The energetic results indicate that the stability of the cycloadducts decreases on proceeding from O, through S and onto Se as confirmed by the analysis of their molecular orbitals. Moreover, we determined the pattern of the lowest singlet and triplet electronic states of these species. We proposed an explanation for the regioselectivity of these reactions for the selective products.