A Novel Route to 2,3-Pyrazol-1(5H)-ones via Palladium-Catalyzed Carbonylation of 1,2-Diaza-1,3-butadienes

reaction--see text A novel Pd(0)-catalyzed carbonylation of both isolable 1,2-diaza-1,3-butadienes and those generated in situ by extrusion of SO(2) and CO(2) from heterocyclic precursors is described. The reaction proceeds at room temperature to 110 degrees 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.