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The electronic reorganization along the 3+2 cycloaddition (32CA) reaction of the simplest azomethine ylide (AY) with ethylene has been studied using the topological analysis of the ELF at the B3LYP/6-31G(d) level of theory. This 32CA reaction, which has a negligible barrier (1.2 kcal/mol), takes place through a synchronous concerted transition state structure. The analysis of the ELF stresses that the pseudo-diradical character of the AY is responsible for the large reactivity of this species. Only the two non-bonding electrons located at the terminal carbon atoms of the AY and the two π electrons of ethylene are involved in this 32CA reaction. This cycloaddition, certainly not a pericyclic electron reorganization, may be electronically classified as 2n + 2π process. Keywords: 3+2 cycloaddition, pseudo-diradicals, 2n + 2π cycloaddition, azomethine ylides, reaction mechanism, ELF analysis
Domingo et al. (Thu,) studied this question.