5-Chloropyrazolo[1,5-a]pyrimidine

29274-22-4

29274-24-6

General procedure for the synthesis of 5-chloropyrazolo[1,5-a]pyrimidin-5-ol from pyrazolo[1,5-a]pyrimidin-5-ol: Pyrazolo[1,5-a]pyrimidin-5-ol (17.0 g, 126 mmol) was dissolved in phosphorus triclosan (100 mL) and heated to reflux for 3 hours. Upon completion of the reaction, the reaction was cooled to room temperature and the reaction mixture was concentrated under reduced pressure to remove excess phosphorous trichloride. Dichloromethane (100 mL) was added to the residue to dissolve it, followed by careful washing of the organic phase with saturated aqueous sodium bicarbonate solution (100 mL x 3) to neutralize acidic impurities. The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give the crude product. The crude product was purified by short silica gel column chromatography, using 50% ethyl acetate in hexane solution as eluent, the target fraction was collected and concentrated under reduced pressure to give 5-chloropyrazolo[1,5-a]pyrimidine (13.1 g, 68% yield).