The first example of a tandem thionation/S-cyclization process leading to benzo[c]thiophene-1(3H)-thione and 1H-isothiochromene-1-thione derivatives, starting from 2-alkynylbenzoic acids, is reported. The reaction is carried out in CH₂Cl₂ using 1 equiv. of Lawesson's reagent under MW irradiation at 100 °C and 300 W for 1 h. Depending on the nature of the substituent at the distal β carbon of the triple bond, either benzothiophenethiones or isothiochromenethiones were obtained selectively, in high to excellent yields. The structure of the representative compounds has been confirmed by X-ray diffraction analysis.