Unveiling the atropoisomerism induced facial selectivity and regioselectivity in the [3 + 2] cycloaddition reaction of benzonitrile oxide with 5-methylenehydantoin from the molecular electron density theory perspective

Abstract

The [3 + 2] cycloaddition (32CA) reaction of benzonitrile oxide BNO with 5-methylenehydantoin (MH) has been studied with the MEDT perspective at the DFT/B3LYP/6–31 + g(d,p) level of theory. Topological analysis of the ELF shows zwitterionic character of this 32CA reaction and the non-polar character is revealed form the global electron density transfer (GEDT) calculations at the TSs, consistent with the calculated high relative free energies between 27.6 and 39.1 kcal mol−1. The energetically predicted regioselectivity and atropisomerism induced facial selectivity towards anti isomer is in complete agreement with the experimental outcome. The activation energy in this 32CA reaction is associated with the creation of non-bonding electron density at N2 nitrogen and pseudoradical center at C3 and the formation of new CC and CO covalent bonds were not observed at the TSs which was in conformity with the calculated total electron density and the positive Laplacian of electron density at the bond critical points observed at the interatomic bonding regions of the TSs.