Quaternary Carbon Center Forming Formal [3 + 3] Cycloaddition Reaction via Bifunctional Catalysis: Asymmetric Synthesis of Spirocyclohexene Pyrazolones.

A variety of spirocyclohexene pyrazolones were synthesized in good yields with excellent stereoselectivities through an asymmetric, intermolecular, quaternary carbon center forming [3 + 3] cycloaddition reaction catalyzed by a bifunctional catalyst. The vinylogous pyrazolones used as binucleophilic synthons in this reaction exhibited superior ability for constructing pyrazolone related spirocyclic scaffolds.