1224944-51-7

67-56-1

1224944-46-0

1224944-51-7

5-Oxo-4,5-dihydropyrazolo[1,5-a]pyrimidine-3-carboxylic acid (151 mg, 0.84 mmol, 1.0 eq.) was mixed with phosphorus trichloride (20 mL) and N,N-diisopropylethylamine (440 μL, 2.5 mmol, 3.0 eq.) and heated at reflux for 2 hours. Upon completion of the reaction, the mixture was cooled to room temperature and allowed to stand overnight, followed by concentration under reduced pressure. The concentrated residue was dissolved in methanol (20 mL), stirred for 30 minutes and concentrated again under vacuum. The residue was partitioned between ethyl acetate and water, the organic phase was separated, washed with brine, dried over anhydrous sodium sulfate, filtered through a silica gel pad and finally concentrated to give methyl 5-chloropyrazolo[1,5-a]pyrimidine-3-carboxylate (160 mg, 90% yield). The product was analyzed by LCMS (ESI), m/z [M+H]+ = 212.2; 1H NMR (400 MHz, DMSO-d6) δ: 9.34 (d, 1H), 8.68 (s, 1H), 7.42 (d, 1H), 3.83 (s, 3H).