The pseudoradical (pr)-type azomethine ylide and ethylene can undergo the [3+2] cycloaddition to form regioisomeric pyrrolidines. Domingo and coworkers suggested that the pseudoradical nature of azomethine ylide is the primary reason for the low activation energy barrier (1.2 kcal/mol) of the above cycloadditon reaction. Here, the reactant structure consisted of The EDC plots in panels (d) and (e) of Fig. confirmed the concerted mechanism of this cycloaddition reaction. During the transition from the reactant to TS, the π bond of ethylene and π orbitals of azomethine ylide lost some electron density (shown in magenta). At the same time, two nascent bonds with an equal amount of electron density could be seen (marked blue) between two fragments. During the subsequent transformation from the TS to product, two single bonds between ethylene and azomethine ylide fragments were completely formed (shown in blue), whereas the π orbitals of both ethylene and azomethine ylide orbitals were significant donors of the electron density (shown in magenta).