o-Benzenedisulfonimide has been used for the first time as a Brønsted acid catalyst to induce electrocyclization of dienones into cyclopentenones (Nazarov reaction). The catalyst has been used in various organic solvents or under solvent-free conditions and it is entirely recoverable from the reaction mixture. The versatility and the effectiveness of the proposed procedure is demonstrated on a wide range of both activated and inactivated substrates.