Generation of oxodiazonium ions 3. Synthesis of [1,2,5]oxadiazolo[3,4-c]cinnoline-1,5-dioxides

A reaction of 4-(N-nitramino)-3-phenylfuroxane with the Ac2O/H2SO4 system leads to the formation of [1,2,5]oxadiazolo[3,4-c]cinnoline-1,5-dioxide, the first representative of furoxanocinnolines. The reaction presumably proceeds through the transformation of the nitramine fragment NHNO2 to the oxodiazonium ion [N=N=O](+) with subsequent intramolecular attack by this cation on the phenyl ring. Furoxanocinnoline is also formed in the reaction of the 4-(N-nitramino)-3-phenylfuroxane O-methyl derivative with H2SO4. It is assumed that this reaction also proceeds with involvement of the intermediate cation [N=N=O](+) formed by the protonation of the N=N(O)OMe group and subsequent elimination of MeOH. 7-Nitro derivative is formed when furoxanocinnoline is nitrated with the concentrated HNO3/H2SO4 mixture. The compounds obtained were characterized by H-1, C-13, and N-14 NMR spectroscopy.