Reaction of the furo[2,3-e]pyrido[l,2-b]-as-triazinium salt 1 with methyl hydrazine gave the zwitterionic 1-substituted pyrido-pyridazino-as-triazine 4. The neutral 2-substituted isomer 6 was formed when 1 was treated with 1-formyl-1-methylhydrazine. Reaction of 1 with 1-acyl-2-methylhydrazine gave rise to 1,3,4-trisubstituted zwitterionic derivatives of the same ring system. Efforts to synthesize aryl-substituted zwitterions led to simultaneous formation of the desired compound 12 and of a new ring transformation product, the pyrazolopyrido-astriazine derivative 15.
Recently, we reported that furo[2,3-e]pyrido[l,2-b]-as-triazinium salt 1 reacts with arylhydrazine to give the ringopened hydrazone 2, which can subsequently be cyclized to the fused pyridazine compound 3 of blue color2). To prepare further derivatives on extension of this reaction seemed to be of interest, and 1 was therefore treated with methyl hydrazine. Unexpectedly, the reaction mixture rapidly changed color to deep green indicating a different course of the reaction compared to the earlier cases (i. e. to formation of the yellow hydrazone 2).
Scheme 1 2 T ArNHNH2 3 Spectroscopic analysis of the green crystals obtained from this reaction mixture revealed that, although the structure of the new compound is reminiscent of 2,3-diaryl-2H-pyrido[l,2-b]pyridazino[3,4-e]-as-triazine (3), the methyl group derived from the reagent is attached to N-1 instead of to N-2, and compound 4 was formed in one step.