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Step B: Preparation of ethyl 5-chloropyrazolo[1,5-a]pyrimidine-3-carboxylate; Ethyl 5-oxo-4,5-dihydropyrazolo[1,5-a]pyrimidine-3-carboxylate (22.7 g, 110 mmol) was suspended in phosphorus triclosan (100 mL) and heated to reflux. After maintaining the reflux reaction for 2 h, the reaction mixture was cooled and the excess phosphorous trichloride was removed by distillation under reduced pressure. The residue was diluted with dichloromethane (100 mL) and slowly poured into a flask containing ice water. The organic and aqueous layers were separated and the aqueous layer was further extracted with dichloromethane. All organic phases were combined, dried with anhydrous magnesium sulfate, filtered and concentrated to give ethyl 5-chloropyrazolo[1,5-a]pyrimidine-3-carboxylate (24.2 g, 97.6% yield) as a light yellow solid. Mass spectrum (APCI) m/z = 225.9 (M + H).