From the data in Figure , it becomes evident that metal-free ylide INT2 involved in the [ interaction using the Second-Order Perturbation Theory (SOPT) of the NBO method (Figure ). Furthermore, the barrier associated with the formation of 3a from INT2 is 5.3 kcal/mol lower than that associated with the formation of 4a from INT1 (Figure ). This noticeable difference in the calculated activation energies for the two potential reaction pathways and the occurrence of the NCIs, which stabilize the key ylide intermediates, lead to the preferred formation of 3a over 4a, despite the fact that the latter species is significantly favored thermodynamically. The barrier to interconversion between INT1 and INT2 (7.6 kcal/mol, Figure ) is reinforced by the lower barrier (G ≠ = 1.5 kcal/mol) computed for the generation of the observed product 3a.