<p>A novel eliminative transformation of diazonitroacetanilides to <i>N</i>-arylnitrous amides (<i>N</i>-arylnitrosoamines) was observed and investigated under thermal conditions. Control and crossing-reactions, tracing reaction mixtures, and mechanistic investigations revealed that the eliminative transformation is an intermolecular rearrangement of two molecules of diazonitroacetanilides to <i>N</i>-arylnitramides by loss of two molecules of diazoketene, and further reaction of <i>N</i>-arylnitramides and diazoketene gives rise to <i>N</i>-arylnitrous amides and 3-diazooxiran-2-one under catalyst-free heating conditions. The current reaction provides a new rearrangement and reaction route of diazonitroacetanilides.</p> Graphical abstract <p></p>