Cyano-tetrazole is
the first reported compound that bears four
nitrogen atoms in a single five-membered ring. This unique molecular
scaffold has long been ignored after its discovery in 1885, mainly
attributed to the scarcity of available synthetic methods. Indeed,
the most popular approach to tetrazoles (that is the cycloaddition
reaction between nitriles and azides) has inevitably excluded the
possibility of introducing valuable cyano groups to decorate the final
heterocyclic cores. Here, we describe a completely different disconnection
strategy to the long time-pursued cyano-tetrazoles via a simple, direct,
and practical cycloaddition transformation between readily accessible
aryl diazonium salts and diazoacetonitrile. This method provides both
regioisomers of disubstituted tetrazoles from the same set of starting
materials in a metal cation controlled fashion.