Head‐to‐Tail Dimerization of N‐Heterocyclic Diazoolefins

The head‐to‐tail dimerization of N‐heterocyclic diazoolefins is described. The products of these formal (3+3) cycloaddition reactions are strongly reducing quinoidal tetrazines. Oxidation of the tetrazines occurs in a stepwise fashion, and we were able to isolate a stable radical cation and diamagnetic dications. The latter are also accessible by oxidative dimerization of diazoolefins. Methanol induces a head‐to‐tail dimerization of N‐heterocyclic diazoolefins. The products of these formal (3+3) cycloaddition reactions, quinoidal tetrazines, are strong organic reducing agents.