Ethyl 2,4-dioxovalerate

• 1H-pyrazolo-[3,4-d]-pyridazin-7(6H)-one core analog
• pyrazole

95-92-1

67-64-1

615-79-2

1. Sodium ethoxide (30.0 g, 0.45 mol) was slowly added to 300 mL of anhydrous ethanol under the condition of an ice-salt bath and stirred uniformly. 2. Acetone (14.7 g, 0.3 mol) was pre-mixed with diethyl oxalate (46.7 g, 0.32 mol) to form a mixed solution. 3. Under the condition of keeping the reaction temperature lower than -5° C., the above mixed solution was added to the sodium-ethanol-ethanol solution dropwise with continuous stirring for 3 hours. 4. Upon completion of the reaction, the reaction mixture was slowly poured into ice-water. 5. Add the above mixed solution dropwise to the sodium ethanolate-ethanol solution with continuous stirring for 3 h. 4. Upon completion of the reaction, the reaction mixture was slowly poured into ice water. 5. Adjust the pH of the mixture with 1 mol/L hydrochloric acid to about 4. 6. Extract the aqueous phase using ethyl acetate (EA). 7. Combine the organic layers and wash twice with 150 mL of water, followed by drying with anhydrous sodium sulfate (Na2SO4). 8. The dried organic layer was filtered and concentrated under reduced pressure to give 46.5 g of a yellow liquid product (1a) in 94% yield and 96% purity. 9. The product 1a was used directly in the subsequent reaction without further purification. 10. A similar method can be used to synthesize compounds 1b-h.