Theoretical investigation of the PX3 (X=F, Cl, Br) catalyst effect on the Nitroso‒Diels‒Alder Reaction

The Nitroso‒Diels‒Alder (NDA) cycloaddition reaction between H3C=NO and 1,3‒butadiene catalyzed by a PX3 (X = F, Cl, Br) Lewis acid was characterized using density functional theory calculations. Calculations showed that the smallest values of the activation energies belong to the reaction that catalyzed by PCl3. The activation energy of the studied reactions was decreased within 8.96, 9.77 and 8.6 kcal.mol‒1 in the presence of PF3, PCl3 and PBr3 catalysts, respectively. Investigations showed that the noncovalent bonding between the P atom of PX3 and the O atom of H3C=NO, is adequately capable to active the NDA reaction. The natural bond orbital (NBO) analysis were implemented to understand the nature of C4,Cbut…ORNO and C1,Cbut…NRNO bonds at the TS structures.