Phosphine-Catalyzed Cascade Reaction of Unsaturated Pyrazolones with Alkyne Derivatives: Efficient Synthesis of Pyrano[2,3-c]pyrazoles and Spiro-cyclopentanone-pyrazolones

A triphenylphosphine-catalyzed cascade reaction of unsaturated pyrazolones with dialkyl acetylenedicarboxylates or but-3-yn-2-one to synthesize the bioactive pyrano[2,3-c]pyrazoles in moderate to excellent yields has been developed. Meanwhile, spiro-cyclopentanone-pyrazolones were also first constructed by the triphenylphosphine-catalyzed cascade reaction of unsaturated pyrazolones with 4-phenylbut-3-yn-2-one in moderate to good yields.