There are a lot of nitrogen sources in chemical synthesis and they come in great variety, serving the insatiable appetite of reductions, oxidations, and redox neutral transformations. It is good to see how bond-breaking and making events are orchestrated around the needs of some reagent that contains the “active” form of nitrogen. I particularly like reading about cases wherein nitrogen transfer stems from nitrogen-heteroatom bond breaking. In these instances, I turn a blind eye on low atom economy. Who cares? All I want to see is “molecular gymnastics”. Below is an instructive recent transformation, whose sequence I abbreviate for clarity’s sake. My appreciation of this synthesis of a fused pyridine ring system has to do with how an azo compound undergoes in situ transformation into a diaziridine oxidant, which leads to the eventual scission of the N-N bond during electrophilic aromatic substitution. What we see here is a fairly rare side of azodicarboxylate, which is a common component of redox condensations such as Mitsunobu reaction.

http://pubs.acs.org/doi/abs/10.1021/acs.orglett.6b00456