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How to Form Two Bonds in Three Ways: Reaction Trinity of σ,π-Heterosymmetric Diradicals
Haonan Cheng1, Yun Zeng1, Xiaofan Zhang1
1Shanghai Key Laboratory of Advanced Polymeric Materials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, P. R. China.
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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.
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