Preparation of β²‑Homologous Amino Acids Bearing Polar Side Chains via a Collective Synthesis Strategy

β-Homologous amino acids (βhAAs) are a valuable class of building blocks for novel analogues of bioactive peptides. Thus, practical methods to synthesize enantiopure βhAAs are desirable. We report the application of a collective synthesis strategy to prepare protected β2-homologous amino acids with polar side chains. In this approach, a core structure is constructed via proline-catalyzed Mannich reaction and subsequently derivatized to furnish more than one protected β2-homologous amino acid with a proteinogenic side chain.