The synthesis, spectra, and reactions of some S-alkylthiophenium salts

Abstract

S-Alkyl-thiophenium, -benzo[b]thiophenium and -dibenzo[b,d]thiophenium salts have been obtained by treatment of the corresponding thiophens with alkyl halides in the presence of silver tetrafluoroborate, or similar reagents. Their u.v. spectra resemble those of corresponding sulphoxides and sulphones, rather than those of the parent thiophen. The n.m.r. spectrum of 3-bromo-1-ethylbenzo[b]thiophenium tetrafluoroborate and those of similar compounds show that the ethyl groups appear as ABX₃ systems, which have been computer-simulated. It is concluded that the S-alkyl groups are not coplanar with the sulphur-containing rings. In the mass spectrometer the S-alkyl group is very readily lost but expansion of the thiophen ring also occurs. The salts are powerful alkylating agents.