Hindered ester formation by Sɴ2 azidation of N-acetoxy-N-alkoxyamides and N-alkoxy-N-chloroamides - novel application of HERON rearrangements

Treatment of N-acetoxy-N-alkoxyamides or N-alkoxy-N-chloroamides with sodium azide in aqueous acetonitrile results in Sɴ2 displacement of chloride and the formation of reactive N-alkoxy-N-azidoamides. The reaction with N-acetoxy-N-benzyloxybenzamide has been studied kinetically (k294 = 2 L mol⁻¹ s⁻¹) and azidation of N-formyloxy-N-methoxyformamide has been modeled computationally at the pBP/DN*//HF/6-31G* level of theory. The anomeric amides N-alkoxy-N-azidoamides decompose intramolecularly and spontaneously to esters and two equivalents of nitrogen. This extremely exothermic process facilitates the formation, in excellent yields, of highly hindered esters.