Synthesis of a New Family of 1,1-Diazidoethenes: One-Pot Construction of 4-Azido-1,2,3-triazoles via Nitrene Cyclization.

The reaction of 4,4-dichloro-1,2-diazabuta-1,3-dienes with sodium azide has been studied and found to provide straightforward access to extremely rare 1,1-bisazides. It was demonstrated that these highly unstable compounds are prone to eliminate the N molecule to cyclize into 4-azido-1,2,3-triazoles bearing two aryl (heteroaryl) groups at positions 2 and 5. The formation of bisazides was confirmed by their trapping with cyclooctyne and B3LYP calculations. Most likely, the elimination of nitrogen to form an intermediate nitrene is facilitated by the aza group via anchimeric-like participation. The reaction was found to be very general for the highly efficient synthesis of various 4-azidotriazoles. It was demonstrated that these heterocycles are highly attractive building blocks for subsequent preparation of 1,2,3-triazole-derived compounds.