The reaction of diphenylcyclopropenone with R1N=C(R2)X (2) (R1, R2= alkyl, aryl, X=MeO, EtO, MeS, or Me2N) gave 2-pyrrolin-4-one (3) in good yield. The less reactive carboximidothioate (2, R1=4-MeC6H4, R2=Ph, X=MeS) yielded isomeric 3-pyrrolin-2-one together with 3.