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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. Comment: In the reaction of cyclohexanone and benzaldehyde, the water-swollen 5 was superior in reaction rate and stereoselectivity to the other polymeric prolines 1–4. TGA analysis of the waterswollen 5 showed up to 24% water content in weight. Theoretical calculation suggested that water molecules formed a hydrogen-bonding network between the triazole and the amino acid group in 5. High yields, enantioselectivities, and diastereoselectivities were achieved in the reaction of cyclic ketones and aromatic aldehydes with 5 in water except for the reaction of 4-methoxybenzaldehyde. The catalyst was recycled and reused at least five times without loss of catalytic activity. N N N O NH CO2H

Aldol Reaction in Water Catalyzed with Polymer-Supported Proline