Both Amide-Bearing α- and β-Amino Acids from Natural Aspartic Acid Are Efficient Organocatalysts for Enantioselective Aldol Reactions

Abstract This work aims to compare and explore the different catalytic efficiencies of structurally similar α- and β-amino acids in an asymmetric aldol transformation. Interestingly, aspartic acid is not only an α-amino acid, but also a β-amino acid. Thus, by modifying one of the two acidic groups of aspartic acid, two sets of α- and β-amino acids, 14 amino acids in total, were prepared and used as organocatalysts. The two types of amino acid, interestingly, achieved similar high catalytic efficiencies in the asymmetric aldol transformation under different optimal conditions. The ideal β-amino acid, in some cases, even achieved significantly higher enantioselectivity than the ideal α-amino acid, although α-amino acids are extensively demonstrated to be highly efficient organocatalysts in this asymmetric transformation.