2‑Methylmercaptothiophene as heterocyclic thioanisole analogue is transformed by dissolving in trifluoracetic acid, instead into a S or C protonated species, into a dimeric compound with a tetrahydrothiophene unit. This finding has been derived from appropriate ¹H NMR and mass spectra and stands in analogy to the oligomerisation of the parent thiophene with polyphosphoric acid.