Literature examples illustrating the use of oxalyl chloride to prepare dicarboxylicacid anhydrides are surprisingly limited. At the same time, we have discovered a method involving the use of this readily available reagent which allowed the preparation of novel cyclic anhydrides where other, more conventional, methods had failed. Herein, we demonstrate that the method is applicable to a wide diversity
3‐(o‐Carboxyphenyl)propionic acid and four of its heteroatom‐containing analogs, as well as benzene‐ring‐fused analogs, have been shown to undergo a Castagnoli–Cushman reaction when dehydrated in the presence of an imine using aceticanhydride. This provides a facile, diastereoselective route to skeletally diverse arene‐fused ε‐lactams.