Aldol Reaction in Water Catalyzed with Polymer-Supported Proline

Significance

Polystyrene-support prolines (1-5) were prepared by the cycloaddition of the corresponding azides and alkynes. Prolines 1-5 catalyzed the aldol reaction of cyclohexanone with benzaldehyde in water to give the aldol product 6 in traces to 74% yield with 40-98% ee. When proline 5 was used for the reaction, a gel-like single phase was formed in water. Water-swollen proline 5 showed higher catalytic activity for the aldol reaction of cyclohexanone and 4-nitrobenzaldehyde (99% yield and 96% ee) than anhydrous 5 (80% yield and 89% ee). The aldol reaction of cyclic ketones with various aldehydes was also catalyzed by 5 in water at room temperature to afford the corresponding products in 16-99% yield and 94-99% ee.