The stereoselective
synthesis of spirocyclic pyrazolin-5-ones by
N-heterocyclic carbene (NHC) organocatalysis has been less studied
so far. For this reason and considering the interest of this class
of compounds, here, we present the NHC-catalyzed [3 + 2]-asymmetric
annulation of β-bromoenals and 1H-pyrazol-4,5-diones
that achieves to produce chiral spiropyrazolone-butenolides. The synthesis
is general for aryl and heteroaryl β-bromo-α,β-unsaturated
aldehydes and 1,3-disubstituted pyrazolones. The spirobutenolides
have been obtained in good yields (up to 88%) and enantioselectivities
(up to 97:3 er). This constitutes the first described example using
pyrazoldiones as the starting materials for this class of spiro compounds.