A new facile synthesis of 5-arninopyridazine-4-carboxylic acid

Hofmann rearrangement of 5-carbamylpyridazine-4-carboxylic acid ( 6 ), obtained from pyrida-zine-4,5-dicarboxylic acid ( 3 ) through the corresponding anhydride ( 5 ), afforded 5-aminopyrida-zine-4-carboxylic acid ( 1 ) in good yield. Compound 1 cyclised with benzoyl chloride in pyridine to give 2-phenylpyridazino[ 4 ,5-d]-1,3-oxazin-4-one ( 7 ), a new heterocyclic ring system. J. Heterocyclic Chem., 14, 1099 (1977)