Asymmetric Construction of Bis‐Spirocyclic Pyrazolones Bearing Vicinal Quaternary Carbon Centers.

A catalytic asymmetric (3+2) cyclization of pyrazolone‐based MBH adducts with alkylidenyl isoxazolones was presented by using DMAP‐derived chiral catalyst, affording bis‐spirocyclic pyrazolones bearing vicinal all‐carbon quaternary stereocenters within an imbedded cyclopentene ring scaffold in good yields with excellent stereoselectivities under mild conditions. [ABSTRACT FROM AUTHOR]