4-Substituted prolines as organocatalysts for aldol reactions

A series of 4-substituted prolines were prepared and evaluated as organocatalysts for asymmetric aldol reactions. Using (2S,4R)-4-camphorsulfonyloxy-proline, the aldol products were obtained in much higher enantiomeric excess in comparison to that observed using proline itself. In addition, the improved solubility of these new catalysts in organic solvents permits their use in lower sub-stoichiometric amounts compared to proline.