Condensed pyridazines. Part II. Synthesis of pyrido[2,3-C] pyridazines

The synthesis of some pyrido2,3-c]pyridazines from 5,8-diehloro-3-methyl-2-oxo-2H-pyrano-2,3-d]pyridazine (I) is described. Attempted oxidation of 8-amino-3-chloro-1,6-dimethyl-4,7-dioxo-1,4,7,8-tetrahydropyrido2,3-c]pyridazine (VI) with LTA led only to the deaminated compound VII. Treatment of VI with LTA A in the presence of cyclohexene gave the nitrene adduct XI.