A novel Pd (0)-catalyzed carbonylation of both isolable 1, 2-diaza-1, 3-butadienes and those generated in situ by extrusion of SO2 and CO2 from heterocyclic precursors is described. The reaction proceeds at room temperature to 110° C under 1-2 atm of CO to afford 2, 3- pyrazol-1 (5H)-ones in good to excellent yields. The effect of catalyst structure and stability on the carbonylation reaction is evaluated.