N-Fluoropyridinium Salts, Synthesis and Fluorination Chemistry

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Synthesis of N-fluoropyridinium salts and their synthetic application are discussed. Various types of stable N-fluoropyridinium salts are synthesized from unsubstituted and substituted pyridines and acids, their salts, silyl esters or Lewis acids by reaction with F2 diluted with N2. The N -fluoropyridinium salts are particularly useful as electrophilic fluorinating agents toward organic compounds in terms of easy handling and variability of fluorinating power and selectivity. This variability makes selective fluorination of a wide range of organic compounds differing in reactivity possible. Three classes of power- and selectivity-variable fluorinating agents, non-counterion-bound N-fluoropyridinium salt series, counterion-bound N-fluoropyridinium-sulfonate series, and dimeric N,N’- difluorobipyridinium salt series, were developed and successfully utilized for selective fluorinations of various substrates. As another synthetic application, a novel base-initiated reaction of N-fluoropyridinium salts producing α- fluoropyridines is discussed.