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General procedure for the synthesis of 5-chloropyrazolo[1,5-a]pyrimidin-7(1H)-ones from 5,7-dichloropyrazolo[1,5-a]pyrimidines: 1 g of 5,7-dichloropyrazolo[1,5-a]pyrimidines was suspended in 25 mL of 1 N aqueous sodium hydroxide solution, heated to 90 °C and stirred for 0.5 h. The reaction was carried out by thin layer chromatography (TLC). The progress of the reaction was monitored by thin layer chromatography (TLC). After completion of the reaction, the reaction mixture was cooled to room temperature. The pH was adjusted to 2 with 1N HCl solution to form a suspension. 5-Chloropyrazolo[1,5-a]pyrimidin-7(1H)-one (0.9 g, 99% yield) was obtained by filtration after standing.

[1] Patent: CN107033149, 2017, A. Location in patent: Paragraph 0110; 0180-0181
[2] Journal of Heterocyclic Chemistry, 1985, vol. 22, # 3, p. 601 - 634