The effect of the PCl3 as a catalyst on the Hetero‒Diels‒Alder reaction between Urea or Iso‒Urea with 1,3‒butadiene

Using density functional theory (DFT), we show that PCl3 is capable to catalyze the a Hetero‒Diels‒Alder (HDA) reaction between urea [(NH2)2C=O] or iso‒urea [NH2OHC=NH] with 1,3‒butadiene. The PCl3 through the pnicogen bonding between their P atom with the O atom of urea or the N atom of iso‒urea catalyze the HAD reaction. The results show that pnicogen bonding of PCl3 has more catalytic effects on activation energy of urea and 1,3‒butadiene in comparison with iso‒urea and 1,3‒butadiene. The natural bond orbital (NBO) analysis on the TS structures were used to understand the nature of the interactions between urea and iso‒urea with 1,3‒butadiene in the presence and absence of the PCl3 as catalyst.