Ethyl 5-oxo-4,5-dihydropyrazolo[1,5-a]pyrimidine-3-carboxylate

Ethyl 5-oxo-4,5-dihydropyrazolo[1,5-a]pyrimidine-3-carboxylate is a heterocyclic organic compound, appearing as a solid, known as an important intermediate in synthesizing biologically active pyrazolopyrimidines, often used in anticancer research for creating kinase inhibitors.

Ethyl 5-oxo-4,5-dihydropyrazolo[1,5-a]pyrimidine-3-carboxylate is mainly used in organic synthesis and drug development.

Ethyl 3-amino-1H-pyrazole-4-carboxylate (25.0 g, 161 mmol) was mixed with ethyl (E)-3-ethoxyacrylate (35.8 mL, 242 mmol) in N,N-dimethylformamide (DMF, 537 mL). Cesium carbonate (78.7 g, 242 mmol) was added to the mixture, and the reaction system was then heated to 110 °C for 15 hours. After the reaction was complete, the mixture was cooled to room temperature and the pH was adjusted to 4 with acetic acid (HOAc). The precipitate was collected by filtration and washed with water and ethyl acetate (Chemicalbook EtOAc) to give ethyl 5-oxo-4,5-dihydropyrazolo[1,5-a]pyrimidine-3-carboxylate as a fluffy white solid. Additional product was recovered by aqueous workup. The filtrate was concentrated to remove DMF, diluted with EtOAc (500 mL), and washed with deionized water. The precipitate in the EtOAc layer was filtered and washed with water and EtOAc to obtain additional product. All solid products were combined and dried in vacuo to obtain 5-hydroxypyrazolo[1,5-a]pyrimidine-3-carboxylic acid ethyl ester (33.3 g, yield 100%). 3-Amino-1H-pyrazole-4-carboxylic acid ethyl ester (25.0 g, 161 mmol) and (E)-3-ethoxyacrylate ethyl ester (35.8 mL, 242 mmol) were mixed in N,N-dimethylformamide (DMF, 537 mL). Cesium carbonate (78.7 g, 242 mmol) was added to the mixture, and the reaction system was then heated to 110 ° C for 15 hours. After the reaction was completed, the mixture was cooled to room temperature and the pH was adjusted to 4 with acetic acid (HOAc). The precipitate was collected by filtration and washed with water and ethyl acetate (Chemicalbook EtOAc) to give ethyl 5-oxo-4,5-dihydropyrazolo[1,5-a]pyrimidine-3-carboxylate as a fluffy white solid. Additional product can be recovered by aqueous post-treatment. The filtrate was concentrated to remove DMF, diluted with EtOAc (500 mL), and washed with deionized water. The precipitate in the EtOAc layer was filtered and washed with water and EtOAc to give additional product. All solid products were combined and dried in vacuo to finally obtain ethyl 5-hydroxypyrazolo[1,5-a]pyrimidine-3-carboxylate (33.3 g, 100% yield).

[1] Patent: WO2011/6074, 2011, A1. Location in patent: Page/Page column 70