Diastereo- and Enantioselective Organocatalytic Synthesis of Spirocyclopropyl Pyrazolones

A diastereo- and enantioselective synthesis of spirocyclopropylpyrazolones has been described through a Michael/alkylation cascade reaction of 4-arylidenepyrazol-5-ones with diethyl 2-bromomalonate catalyzed by (DHQ)(2)AQN. The reaction afforded selectively the corresponding spirocyclic compounds with 30-83% yield, diastereoselectivities ranging from 60:40 to >95:5 and 26-93% enantiomeric excess under mild reaction conditions. Moreover, we performed two selective transformations with the corresponding chiral compounds.