Under open-vessel atmosphere conditions, a one-pot easy-to-operate method for the construction of diverse sulfonyl dibenzosuberdiones is developed via In(OTf)₃-promoted tandem double Friedel–Crafts reactions of oxygenated arylacetic acids with β-arylvinyl sulfones. A plausible mechanism is proposed and discussed in detail. This protocol allows for highly effective sequential intermolecular Michael addition, intramolecular ring-closure and α-benzylic oxidation via the formation of two carbon–carbon single (C–C) bonds and one carbon–oxygen double (CO) bond.