Four anhydrides of 1-(carboxymethyl)pyrrole-2-carboxylic acids bearing electron-withdrawing substituents at positions 6 or 7 of the bicyclic system have been investigated in the Castagnoli–Cushman reaction with imines. 6-Benzoyl- and 7-sulfamoyl-substituted anhydrides demonstrated lower reactivity while 7-benzoyl derivative displayed broader substrate scope. These findings have been rationalized from the mechanistic perspective.