Polyfluoro-heterocyclic compounds. Part VI. Nucleophilic substitution in tetrafluoro-4-nitropyridine

Abstract

Reaction of tetrafluoro-4-nitropyridine with ammonia and sodium methoxide leads to considerable replacement of the nitro-group, unlike 2,3,5,6-tetrafluoro-4-nitrobenzene which gives exclusive replacement of fluorine ortho to the nitro-group. The pyridine-ring nitrogen is the greatest single factor in determining the orientation of nucleophilic attack. Competition experiments show relative reactivities to be in the order: pentafluoropyridine ≈ pentafluoronitrobenzene > tetrafluoro-4-nitropyridine. Fluorine-19 n.m.r. spectra of derivatives of pentafluoropyridine have been examined but the effect of substituent methoxyl and amino-groups on chemical shifts was not consistent, especially in the presence of a nitro-group.