Synthesis of 1,2,3,4-tetrazino[5,6-f]benzo-1,2,3,4-tetrazine 1,3,7,9-tetra-N-oxides.

[reaction: see text] The novel heterocyclic system 10 with the phenanthrene type skeleton, in which the benzene ring is annulated with two 1,2,3,4-tetrazine 1,3-di-N-oxide rings, is of considerable interest in the context of the high nitrogen system stability and from a heteroaromaticity standpoint. The step-by-step synthetic approach to this system involves treatment of 5 with N2O5, resulting in the first 1,2,3,4-tetrazine 1,3-dioxide ring formation. The following displacement of the chlorine atom at the 6-position with ammonia and subsequent repeated treatment with N2O5 results in the second 1,2,3,4-tetrazine 1,3-dioxide ring formation. The structure of 10 was confirmed by a 13C and 14N NMR study.