Secondary amine-catalyzed [3 + 3] benzannulation to access polysubstituted benzenes through iminium activation

An organocatalytic [3 + 3] benzannulation to access polysubstituted benzenes from readily available α,β-unsaturated aldehydes and 1,3-bis(phenylsulfonyl)propene or 4-sulfonylcrotonates is described. The key reaction step is considered to be the iminium activation of enals by a secondary aminocatalyst. This organocatalytic protocol avoids the traditional strategy which is always with the aid of a transition-metal or a stoichiometric amount of strong base, and allows the synthesis of trisubstituted benzenes in high to excellent yields (74–96%).