σ,π-Heterosymmetric diradicals are typically formed through the Myers–Saito cyclization of enyne-allene, featuring distinct chemical environments for the two radicals. In this study, maleic hydrazide was introduced at the ene position of enediyne molecules, leveraging the electron-withdrawing properties of these groups to facilitate the rearrangement of enediyne into enyne-allene, which subsequently leads to the generation of σ,π-heterosymmetric diradicals through cycloaromatization. Based on experimental results and computational analysis, we identified three competing reaction pathways for σ,π-heterosymmetric diradicals: (1) hydrogen atom abstraction by diradicals, (2) interactions of π-radicals with nucleophiles, and (3) interactions of σ-radicals with nucleophiles. In path 1, both radical centers can readily abstract hydrogens, with the σ-radical, showing a clear preference. In paths 2 and 3, the distortion of the core aromatic ring during the nucleophilic reaction leads to the disruption of the orthogonality of the radical orbitals through the formation of a Möbius-like conjugated framework, providing an efficient pathway for electron transfer and thereby facilitating both diradical quenching and nucleophilic addition.
Cheng et al. (Thu,) studied this question.