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 pyrano2,3‐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.