A computational investigation of the structure of the novel anomeric amide N-azido-N-methoxyformamide and its concerted decomposition to methyl formate and nitrogen

Treatment of N-alkoxy-N-chloro- or N-acetoxyamides with sodium azide in aqueous acetonitrile results in S(N)2 displacement of chlorine or acetate and the formation of reactive N-alkoxy-N-azidoamides which undergo a concerted decomposition to esters and nitrogen. The properties of the model N-azido-N-methoxyformamide have been computed at the B3LYP/6-31G* hybrid density functional level of theory. It is a typical anomeric amide in that the nitrogen is strongly sp(3) hybridised resulting in a low amide isomerisation barrier. It decomposes in a two-step process involving exothermic loss of N-2 to give 1-formyl-1-methoxydiazene which spontaneously undergoes a HERON decomposition to methyl formate and N-2. Overall, the process is highly exothermic (DeltaG between -654 and -659 kJ mol(-1)). The competitive one-step HERON process involving formation of methyl formate and tetrazene is kinetically unfavourable. Sterically hindered ester formation will be facilitated by both exothermicity and a transition state for ester formation which avoids a sterically crowded tetrahedral intermediate.