Abstract magnified image A facile synthesis of bis‐β‐lactams has been executed using chloromethylenedimethylammonium chloride (Vilsmeier reagent), prepared easily from N,N‐dimethylformamide and phosphorus oxychloride. It works out as a versatile acid activator reagent for the direct [2 + 2] ketene–imine cycloaddition of substituted acetic acid and bis‐imines in one‐pot synthesis under mild conditions. Thus, this method has been proved as a high yielding, efficient, and cheap protocol for bis‐β‐lactam synthesis. J. Heterocyclic Chem., (2010).