Novel Prolinamide-Camphor-Containing Organocatalysts for Direct Asymmetric Michael Addition of Unmodified Aldehydes to Nitroalkenes

A new prolinamide-derived organocatalysts 4a-c that contain a structural rigid bicyclic camphor scaffold were used for the first time in organocatalysis. The aldehyde was added to a mixture of catalyst 4b and the corresponding nitroalkene in CHCl3/MeOH. The reaction mixture was stirred at either ambient temperature or 0°C. The reaction mixture was subject to flash column chromatography on silica gel to give a pure Michael product. The enantiomeric excess of Michael products was determined by chiral HPLC analysis. The enantiomeric purity was determined by using Chiralcel OD-H. Both catalysts performed poorly in the reaction between propionaldehyde and trans-β-nitrostyrene, indicating that the hydroxyl group in 4b must play some role in determining the stereochemical outcomes of the reaction.