General procedure for the synthesis of 6-keto-1,6-dihydropyridazine-4-carboxylic acid from 5-methyl-3(2H)-pyridazinone: 5-methyl-3(2H)-pyridazinone (0.90 g, 8.2 mmol) was dissolved in concentrated sulfuric acid (13 mL), stirred and heated to 45 °C. Potassium permanganate (3.6 g, 12 mmol) was added in batches over a period of 30 min to control the reaction temperature to avoid a dramatic increase. After addition, the reaction was continued at 45°C with stirring for 30 minutes. After completion of the reaction, it was cooled to room temperature and quenched by adding ice water to the reaction mixture. The precipitate precipitated was collected by vacuum filtration and washed sequentially with cold water and ether to afford 0.98 g (87% yield) of the target product 6-keto-1,6-dihydropyridazine-4-carboxylic acid as a light green solid. The product was characterized by 1H NMR (300 MHz, CDCl3): δ 13.39 (broad single peak, 1H), 8.12 (single peak, 1H), 7.22 (single peak, 1H).
