Asymmetric Synthesis of Quaternary α- and β-Amino Acids and β-Lactams via Proline-Catalyzed Mannich Reactions with Branched Aldehyde Donors

l-Proline-catalyzed direct asymmetric Mannich reactions of N-PMP protected α-imino ethyl glyoxylate with various α,α-disubstituted aldehydes
affords quaternary β-formyl α-amino acid derivatives with excellent yields and enantioselectivities. The Mannich products are further converted
to the corresponding quaternary α- and β-amino acids and β-lactams.