Polyfluorocarbanion chemistry. Part II. Fluoride-initiated reactions of hexafluoropropene with pentafluoropyridine and tetrafluoropyridine-4-carbonitrile

Abstract

Hexafluoropropene reacts with pentafluoropyridine in a dipolar aprotic solvent in the presence of caesium fluoride to give one mono-(4-), two di-(2,4- and 2,5-), and two tri-(2,4,5- and 2,4,6-) substituted derivatives. The 2,5- and 2,4,5-compounds, unexpected by analogy with other nucleophilic attacks on pentafluoropyridine, are regarded as arising by kinetically controlled reaction to give the 2,4,5-compound, which then undergoes intermolecular rearrangement to the products ultimately obtained by thermodynamic control. The relative stabilisation of the postulated anionic intermediates by α-fluorine or -perfluoroalkyl groups can be deduced. The heptafluoroisopropyl carbanion reacts with tetrafluoropyridine-4-carbonitrile to give one di-(2,5-), two tri-(2,3,5- and 2,3,6-), and the tetra-substituted derivatives. ¹⁹F N.m.r. results indicate the occurrence of strong through-space coupling in these compounds.