Imidazolidinones are catalysts for many transformations such as asymmetric Diels-Alder reactions and Michael additions. Chiral catalysts induce asymmetric reactions, often with high enantioselectivities.  This catalyst works by forming an iminium ion with carbonyl groups of α,β-unsaturated aldehydes (enals) and enones in a rapid chemical equilibrium. This iminium activation is similar to activation of carbonyl groups by a Lewis acid and both catalysts lower the substrate's LUMO:
The transient iminium intermediate is chiral which is transferred to the reaction product via chiral induction. The catalysts have been used in Diels-Alder reactions, Michael additions, Friedel-Crafts alkylations, transfer hydrogenations and epoxidations.
One example is the asymmetric synthesis of the drug warfarin (in equilibrium with the hemiketal) in a Michael addition of 4-hydroxycoumarin and benzylideneacetone:
A recent exploit is the vinyl alkylation of crotonaldehyde with an organotrifluoroborate salt:
For other examples of its use: see organocatalytic transfer hydrogenation and asymmetric Diels-Alder reactions.