Heterocyclic polyfluoro-compounds. Part XXI. Synthesis of some 2-substituted tetrafluoropyridines: 2,3,4,5-tetrafluoro-6-methoxypyridine and 3,4,5,6-tetrafluoropyridine-2-carbaldehyde, -2-carboxylic acid,-2-carboxamide, and -2-carbonitrile

Abstract

3,4,5,6-Tetrafluoropyridine-2-carbonitrile and 3,5-dichloro-4,6-difluoropyridine-2-carbonitrile can be obtained by heating 3,4,5,6-tetrachloropyridine-2-carbonitrile with potassium fluoride. Reduction of the tetrafluorocompound with Raney alloy–aqueous formic acid yields 3,4,5,6-tetrafluoropyridine-2-carbaldehyde (characterised as its oxime), which reacts with oxygen to give 3,4,5,6-tetrafluoropyridine-2-carboxylic acid (perfluoropicolinic acid); acidic hydrolysis of tetrafluoropyridine-2-carbonitrile provides 3,4,5,6-tetrafluoropyridine-2-carboxamide.

Treatment of phenyl 2,3,5,6-tetrafluoropyridyl sulphone with sodium methoxide yields phenyl 2,3,5-trifluoro-6-methoxypyridyl sulphone, which reacts with caesium fluoride in hot tetramethylene sulphone to give 2,3,4,5-tetrafluoro-6-methoxypyridine.