Desymmetrization of Prochiral -Pyrazolyl Maleimides via Organocatalyzed Asymmetric Michael Addition with Pyrazolones: Construction of Tri--Heterocyclic Scaffolds Bearing Both Central and Axial Chirality.

The desymmetrization of -pyrazolyl maleimides was realized through an asymmetric Michael addition by using pyrazolones under mild conditions, leading to the formation of a tri--heterocyclic pyrazole-succinimide-pyrazolone assembly in high yields with excellent enantioselectivities (up to 99% yield, up to 99% ee). The use of a quinine-derived thiourea catalyst was essential for achieving stereocontrol of the vicinal quaternary-tertiary stereocenters together with the C-N chiral axis. Salient features of this protocol included a broad substrate scope, atom economy, mild conditions and simple operation.