A novel palladium(0)-catalyzed domino cyclization of 2-alkynylaziridines with isocyanates through ring expansion is described. Treatment of N-protected 2-(4-aminobut-1-ynyl)aziridine derivatives With a catalytic amount of Pd(PPh(3))(4) and aryl isocyanates in THF at room temperature affords 4-(4,5-dihydropyrrol-2-yl)imidazolidin-2-one derivatives in good yields. Interestingly, bis-adducts were selectively obtained by use of excess isocyanate (5 equiv) at lower reaction temperature.