Sun, QiuEitzinger, AndreasEsken, RobinAntoni, Patrick W.Mayer, Robert J.Ofial, Armin R.Hansmann, Max M.2025-04-032025-04-032023-12-28http://hdl.handle.net/2003/4359010.17877/DE290R-25423Mesoionic polarization allows access to electron-rich olefins that have found application as organocatalysts, ligands, or nucleophiles. Herein, we report the synthesis and characterization of a series of 3-methylpyridinium-derived mesoionic olefins (py-mNHOs). We used a DFT-supported design concept, which showed that the introduction of aryl groups in the 1-, 2-, 4-, and 6-positions of the heterocyclic core allowed the kinetic stabilization of the novel mesoionic compounds. Tolman electronic parameters indicate that py-mNHOs are remarkably strong σ-donor ligands toward transition metals and main group Lewis acids. Additionally, they are among the strongest nucleophiles on the Mayr reactivity scale. In reactions of py-mNHOs with electron-poor π-systems, a gradual transition from the formation of zwitterionic adducts via stepwise to concerted 1,3-dipolar cycloadditions was observed experimentally and analyzed by quantum-chemical calculations.enAngewandte Chemie. International edition; 63(10)https://creativecommons.org/licenses/by/4.0/(3+2) CycloadditionMesoionsN-Heterocyclic OlefinsNucleophilicityYlides540ResearchArticle