Cyclic (Amino)(Aryl)Nitrenium Cations with Lewis Acidity Controlled by Remote Substituents

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Comprehensive Summary N ‐Heterocyclic nitrogen Lewis acids are important in synthetic chemistry. Stable cyclic (amino)(aryl)nitrenium cations, cyc‐1 + —cyc‐3 + , were synthesized by chemical oxidation of aryl azo compounds with different substituents, i Pr, H and I, at the para positions of the phenyl group. The excited triplet states of cyc‐1 + —cyc‐3 + abstract H‐atoms step by step to generate radical intermediates cyc‐1H •+ —cyc‐3H •+ traced by EPR spectroscopy and products cyc‐1H 2+ —cyc‐3H 2+ characterized by single crystal X‐ray diffraction. The Lewis acidity of species cyc‐1 + —cyc‐3 + are remote substituent‐dependent. Cyc‐2 + —cyc‐3 + have much higher acidity than those previously reported congeners based on energies of LUMOs. The electrophilicity enables them to form Lewis adducts with neutral Lewis base Me 3 P, and to gain one‐electron to produce neutral radicals cyc‐1 • —cyc‐3 • .