Single‐Step,Rapid, and Mild Synthesis of β‐Amino Acid N‐Carboxy Anhydrides Using Micro‐Flow Technology

β‐Amino acid N‐carboxy anhydrides (β‐NCAs) are rarely used in the synthesis of β‐peptides, which is due mainly to the poor availability of these potentially useful substrates. Herein, we describe the heretofore challenging synthesis of β‐NCAs via a single‐step, rapid, and mild formation using pH flash switching and flash dilution, which are aspects of micro‐flow technology. We synthesized 15 β‐NCAs in good to excellent yields that included acid‐labile β‐NCAs that cannot be readily synthesized using the conventional Leuchs approach. Scaled‐up synthesis using this process can be readily achieved via continuous operation.