Biomimetic Chemoselectivity Control of Aldol Reactions

The synthesis and utilization of polymeric catalyst 1 bearing proline moieties as active sites is reported. This catalyst aggregate was applied successfully in aldol reactions of aldehydes and ketones in aqueous media. In a self-­aldol process of butanal, mainly reversibly formed β-hydroxyaldehyde 2 was obtained, whereas the formation of aldol condensation product 3 could be suppressed. These results were transferred to more complex dynamic catalytic cross-aldol reactions, giving rise to α,β-unsaturated ketones 4, favored over formation of self-condensation product 5. The likewise expected ketones 6 were not observed.