Unravelling the Mysteries of the [3+2] Cycloaddition Reactions

Abstract

After Huisgen's and Firestone's mechanistic proposals made in the 1960s based on experiments, several theories were proposed during the last century to explain [3+2] cycloaddition (32CA) reactions, most of them still prevailing today. Recent molecular electron density theory (MEDT) studies of 32CA reactions involving representative three‐atom components have allowed characterising at least four different electronic structures, which experience a dissimilar chemical reactivity. In this review, the four simplest reactivity models are presented, providing a modern rationalisation of 32CA reactions based on MEDT.