Synthetic Route to Phenyl Diazenes and Pyridazinium Salts from Phenylazosulfonates

The synthesis of pyridazinium salts was achieved from readily available phenylazosulfonates in a single reaction step. The reaction proceeds via the formation of short-lived phenyldiazenes, which-owing to the strongly acidic conditions-are partially protonated. The phenyldiazenes then undergo a rapid cycloaddition to furans to give pyridazinium salts via elimination of water. The fact that the pyridazinium synthesis shows a low sensitivity toward oxygen, although phenyldiazenes occur as intermediates, can be explained by the very fast cycloaddition step and the partial protonation of the phenyldiazene.

Automated summary

The synthesis of pyridazinium salts from readily available phenylazosulfonates is achieved in a single reaction step. This reaction involves the formation of short-lived phenyldiazenes, which are partially protonated under strongly acidic conditions, and undergo a rapid cycloaddition to furans to give pyridazinium salts via elimination of water. Despite the presence of phenyldiazenes as intermediates, the pyridazinium synthesis shows low sensitivity toward oxygen due to the very fast cycloaddition step and partial protonation of the phenyldiazene.