In this work, regioselectivity was investigated in the hetero-Diels–Alder reactions of styrenes (without substituent and with para-substituted groups)with 2-aza-1,3-butadiene from thermodynamic (Hammett study), electronic (HSAB criterion) and kinetic viewpoints. Furthermore, the effect of the presence of catalyst was inspected by the NBO analysis in addition to kinetic studies. The calculations were performed by the Gaussian 09 program at the B3LYP/6-311++G** level of theory in the gas phase. Thermodynamically, the stability difference between the two regioisomeric products is not significant, especially, in the reactions of styrenes with electron-releasing substituents. Kinetically, the obtained regioselectivity is in favor of formation of 4-regioisomers, especially, in the presence of BF3 catalyst (in agreement with the NBO results). On thebasis of the HSAB criterion, 5-regioisomers have preference, only in the reactions of styrenes with the strong electron-withdrawing substituents.