N-Alkynylpyridinium Salts: Highly Electrophilic Alkyne-Pyridine Conjugates as Precursors of Cationic Nitrogen-Embedded Polycyclic Aromatic Hydrocarbons

摘要

We achieved the first synthesis of N -alkynylpyridinium salts, by reacting pyridines with alkynyl-λ~(3)-iodanes. The N -alkynylpyridiniums exhibit highly electron-accepting character with extended π-conjugation. The electrophilic alkynyl groups were readily susceptible to Michael addition and 1,3-dipolar cycloaddition to afford various N -alkenylpyridiniums. Ring-fused pyridiniums were synthesized through intramolecular cyclization, demonstrating the utility of N -alkynylpyridiniums for the design of various electron-deficient cationic nitrogen-embedded polycyclic aromatic hydrocarbons with unique optical and electrochemical properties.