Highly fluorinated heterocycles. Part V. The preparation and some reactions of tetrafluorothiophen and some polyfluorothiophens

Tetrafluorothiophen has been prepared by dehydrofluorination of 3H/4H-hexafluorothiolan by molten alkali. It did not react with bromine nor did it polymerise rapidly, unlike tetrafluorofuran. It reacted with sodium methoxide with displacement of the 2-fluorine, as was proved by an independent synthesis of the other possible isomer, 2,3,5-trifluoro-4-methoxythiophen. 2,5-Difluorothiophen and 2,5-difluoro-3-methoxythiophen have also been prepared. The methoxythiophens all polymerised rapidly. In the 19F n.m.r. spectra of the polyfluorothiophens, the α-fluorines resonate to high field of the β; also, the 2–5 F–F couplings are large (26–31 Hz).