4-Oxo-4,5,6,7-tetrahydropyrazolo[1,5-a] pyrazine-2-carboxylic acid

951626-95-2

1029721-02-5

The general procedure for the synthesis of 4-oxo-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine-2-carboxylic acid using ethyl 4-oxo-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine-2-carboxylic acid as a starting material was as follows: firstly, a solution of lithium hydroxide monohydrate (2.73 g, 65.0 mmol) was prepared by dissolving the lithium hydroxide monohydrate (2.73 g, 65.0 mmol) in water (30.0 mL). Subsequently, this lithium hydroxide aqueous solution was added to a suspension of ethyl 4-oxo-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine-2-carboxylate (2.72 g, 13.0 mmol) in tetrahydrofuran (THF, 30 mL) and methanol (MeOH, 30 mL), and the reaction was carried out at 0 °C. Next, the reaction mixture was stirred at room temperature overnight. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure. Water (20 mL) was added to the residue to dissolve the solid to obtain a clarified solution. This solution was cooled to 0 °C and concentrated. Then, hydrochloric acid (5.42 mL, 65.0 mmol) was slowly added to adjust the pH to 3, at which point solids were precipitated. The suspension was continued to be stirred at 0 °C for 2 h to promote crystallization. Finally, the white solid product was collected by filtration and dried to afford the target compound 4-oxo-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine-2-carboxylic acid (2.2 g, 93% yield). The structure of the product was confirmed by LC-MS (ESI), m/z: 182.1 [M + H]+.