Ionic-liquid-supported organocatalyst: Efficient and recyclable ionic-liquid-anchored proline for asymmetric aldol reaction

Ionic-liquid-anchored (2S,4R)-4-hydroxyproline 12 catalyzes direct asymmetric aldol reactions with comparable enantioselectivities in DMSO, and with superior enantioselectivities in neat acetone or 2-butanone, than (S)-proline (8) (up to 28% ee difference) itself. Furthermore, the supported catalyst 12 can be easily recycled and reused for at least four times without significant loss of yields and enantioselectivity.