TMSN₃ and PhI(OAc)₂ were found to promote high-yield azide substitution of ethers, aldehydes and benzal acetals. The reaction is fast and occurs at zero to ambient temperature in acetonitrile. However, it is essential for the reaction that TMSN₃ is added subsequent to the mixture of PhI(OAc)₂ and the substrate . A primary deuterium kinetic isotope effect was found for the azidonation of benzyl ethers both with TMSN₃–PhI(OAc)₂ and with IN₃. Also a Hammett free energy relationship study of this reaction showed good correlation with σ⁺ constants giving with ρ-values of −0.47 for TMSN₃–PhI(OAc)₂ and −0.39 for IN₃. On this basis a radical mechanism of the reaction was proposed.