N,N'DIFLUORO-1,4-DIAZONIABICYCLO[2.2.2]OCTANE SALTS, HIGHLY REACTIVE AND EASY-TO-HANDLE ELECTROPHILIC FLUORINATING AGENTS

A series of N,N'-difluoro-1,4-diazoniabicyclo[2.2.2]octane salts were synthesized in a pure form by the fluorination of 1,4-diazabicyclo[2.2 .2]octane with F-2 diluted with N-2 in the presence of a Bronsted acid in fluoro alcohol or acetonitrile or by fluorination followed by a tr eatment with a different Bronsted or Lewis acid. Their complete struct ural assignment was made based on spectral and elemental analyses of t he isolated crystals. A great through-bond interaction between the two N-F's of the salt was observed on (19)FNMR. An assessment was made of the usefulness of N,N'-difluoro-1,4-diazoniabicyclo[2.2.2]octane bis( triflate), bis(HSO4), bis(BF4), and bis(SbF6) salts for electrophilic fluorination; the bis(BF4) salt was demonstrated to be widely applicab le as a highly reactive and easy-to-handle fluorinating agent. Thus, t he bis(BF4) salt readily fluorinated activated aromatics, active methy lene compounds or their salts, substituted styrenes, and vinyl acetate s under mild conditions. It was shown that one N-F of the salt was eff ective for fluorination and that the other N-F played a role to activa te fluorination through the bonds. Thus, the reaction mechanism was di scussed, and fluorination followed by an immediate intramolecular one- electron transfer was suggested.