Reactions involving fluoride ion. Part IV. Synthesis and rearrangement of perfluoroisopropylpyridines

Abstract

Synthesis of perfluoropolyisopropylpyridines by fluoride-ion-initiated reactions of hexafluoropropene with pentafluoropyridine at atmospheric pressure is described. Trisubstitution gives a mixture of perfluoro-2,4,5- and 2,4,6-tri-isopropylpyridines; the ratio of these varies with reaction temperature but the 2,4,5-isomer can be obtained as the principal product. The 2,4,5-isomer is rearranged to the 2,4,6-isomer, together with other products, by heating with caesium or potassium fluoride. Cross-over experiments with heptafluoroquinoline have shown that the mechanism of this rearrangement is entirely intermolecular. The mechanism of the polyfluoroalkylation process is discussed.