Two mesityl thienyl sulfones (5-mesitylsulfonyl-2-methylthiophene and 2- mesitylsulfonylthiophene) undergo the Truce--Smiles rearrangement. However, the thienyl unit (in contrast to the previously studied naphthyl and suhstitutetl phenyl groups) migrates with a change in orientation regardless of the baseholvent system used. The chemistry of 2- mesitylsulfonylthiophene is complicated by the acidity of the open ct position, with 2 equiv ...