A highly efficient organocatalyst for direct Aldol reactions of ketones with aldedydes

L-Proline amides derived from various chiral P-amino alcohols that bear substituents with various electron natures at their stereogenic centers are prepared and evaluated for catalyzing the direct Aldol reaction of 4-nitrobenzalclehyde with acetone. Catalysts with strong electron-withdrawing groups are found to exhibit higher catalytic activity and enantioselectivity than their analogues with electron-donating groups. The presence of 2 mol % catalyst 4g significantly catalyzes the direct Aldol reactions of a wide range of aldehydes with acetone and butanone, to give the beta-hydroxy ketones with very high enantioselectivities ranging from 96% to > 99% ee. High diastereoselectivity of 95/5 was observed for the anti Aldol product from the reaction of cyclohexanone, and excellent enantioselectivity of 93% ee was provided for anti Aldol product from the reaction of cyclopentanone.