N-Halogeno compounds .15. Synthesis of N-fluoroquinuclidinium salts via direct fluorination of quinuclidine Lewis acid adducts, and a comparison of their ''F+'' transfer capabilities

Fluorine smoothly attacks quinuclidine-trifluoroborane, quinuclidine-pentafluorophosphorane, and quinuclidine-sulfur trioxide in acetonitrile at -35 degrees C to give the corresponding N-fluoroquinuclidinium salts NFQ(+)X(-) (X(-)=BF4-, PF6-, and FSO3- respectively; Q = quinuclidine). Like its tetrafluoroborate analogue (NFQ(+)BF(4)(-)), the hexafluorophosphate NFQ(+)PF(6)(-) can also be prepared by direct fluorination of quinuclidine in the presence of the appropriate sodium salt (NaPF6). An alternative route to the tetrafluoroborate involves treatment of NFQ(+)F(-) with boron trifluoride. A comparative study of site-specific electrophilic fluorination of methoxybenzene [--> 1-fluoro-2- and 4-methoxybenzene], 2-hydroxynaphthalene (--> 1-fluoro-2-hydroxynaphthalene and 1,1-difluoro-2-oxo-1,2-dihydronaphthalene),2-nitropropan-2-yl-lithium (--> 2-fluoro-2-nitropropane) and diethyl sodio(phenyl) malonate [--> diethyl fluoro(phenyl) malonate] with all of the NFQ(+) X(-) salts mentioned above, plus the triflate (X(-) = CF3SO3-), revealed that the hexafluorophosphate and triflate are the most easily-handled and effective reagents.