Revolutionary phosgene‐free synthesis of α‐amino acid N‐carboxyanhydrides using diphenyl carbonate based on activation of α‐amino acids by converting into imidazolium salts

α-Amino acids imidazolium salt smoothly reacted with diphenylcarbonate to afford the corresponding urethanes. The urethanes were activated by adding carboxylic acid to undergo selective cyclization, leading to successful development of a new phosgene-free process for synthesizing α-amino acid N-carboxyanhydrides (NCAs).