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.