DNA-encoded chemical libraries (DECLs) are increasingly employed in hit discovery toward proteins of pharmaceutical interest. Protected amino acids are the most commonly used building blocks for the construction of DECLs; therefore, the expansion of reaction scope with the subsequent free amine is highly desired. Here, we developed a robust DNA-compatible diazo-transfer reaction using imidazole-1-sulfonyl azide tetrafluoroborate salt converting a wide range of primary amines into their corresponding azides in good to excellent yields.