Chemodivergent Synthesis of 1,4-Benzo b dithiins and 1,4-Benzodithiafulvenes

We report a chemodivergent synthesis of 1,4-benzobdithiins and 1,4-benzodithiafulvenes from 2-iodoaryl alkynyl sulfides using a NaSH·xH2O/KOH system. In DMF, the reaction affords six-membered 1,4-dithiins, whereas in DMSO, these intermediates undergo a base-promoted ring contraction to the corresponding 1,4-dithiafulvenes. Photophysical and mass spectrometry studies support the idea that this chemodivergence arises from the interplay between S2-/S3• - equilibrium and base availability in each solvent, which governs whether the 1,4-dithiin framework is preserved or undergoes ring contraction to 1,4-benzodithiafulvenes.