l-Valine Dipeptide Organocatalysts with Two Amide Units for the Direct Asymmetric Aldol Reaction in Brine

A series of valine dipeptide organocatalysts containing a primary amine group and two amide units have been developed and evaluated in the direct asymmetric intermolecular aldol reaction of 4-nitrobenzaldehyde and cyclohexanone. When 2,4-dinitrophenol (DNP) was used as an acidic additive, the catalyzed reactions of various aldehydes and ketones gave the corresponding aldol products with moderate to high enantioselectivities (up to 95%) and diastereoselectivities (up to > 99/1, anti/syn) in the presence of 3c in brine.