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The CF3S– anion, generated from thiocarbonyl difluoride or its trimer and caesium fluoride, reacted with pentafluoropyridine (1) at –15 °C to give a high yield of 2,3,5,6-tetrafluoro-4-trifluoromethylthiopyridine (2). When the trimer was used as a precursor of the CF3S– anion, compound (2) reacted further at 20 °C to give a mixture of mono-(2), bis-(3) and (4), and tris-(trifluoromethylthio)(5) substituted fluoropyridines. At 100–110 °C, 2,4,6-trifluoro-3,5-bis(trifluoromethylthio) pyridine (4) was obtained as the only product. On oxidation with CrO3 in conc. sulphuric acid compound (2) gave 2,3,5,6-tetrafluoro-4-trifluoromethylsulphonylpyridine (12), and the oxidation of compound (4) led to a mixture of 2,4,6-trifluoro-3,5-bis(trifluoromethylsulphonyl)pyridine (13) and two isomeric fluoro-3,5-bis(trifluoromethylsulphonyl)pyridinediols (14a) and (14b). The sulphone (12) reacted readily with monomeric CF2S to yield a mixture of compounds (3), (5), and 2,4,5,6-tetrafluoro-3-trifluoromethylthiopyridine (15). The reaction of compound (2) with potassium thiophenolate and potassium phenolate also led to a substitution of fluorines and the CF3S group with the PhS or PhO substituents to give compounds (7)–(11). The sulphone (13) readily reacts with methanol to yield 2,4,6-trimethoxy3,5-bis(trifluoromethylsulphonyl)pyridine (18). The structures of the new pyridine derivatives (2)–(5), (7)–(15), and (18) have been elucidated from the m.s., 19F n.m.r., and 13C n.m.r. spectra. The X-ray molecular structure of derivative (18) has been obtained.
Dmowski et al. (Thu,) studied this question.