α,β-Dehydroamino Acid Synthesis through Proline-Catalyzed Aldol Condensation with a Glycine Schiff Base

A general protocol for the synthesis of α,β-dehydroamino acids and their peptides was developed. Proline efficiently catalyzed an aldol condensation reaction of a glycine Schiff base with a variety of aldehydes. The hydroxy group on the benzophenone imine was crucial for high Z/E selectivity and further transimination for protecting group-free α,β-dehydroamino esters. Peptide elongation of both the C- and N-terminals highlighted the usefulness of our present protocol.