Diethyl Ether → Ethyl 5-chloropyrazolo(1,5-a)pyrimidine-3-carboxylate

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Reaction Conditions

Reaction Steps

To a suspension of 5-oxo-4,5-dihydro-pyrazolo[1,5-a]pyrimidine-3-carboxylic acid ethyl ester (prepared according to Gavrin, L. K. et al, J. Org. Chem. 2007, 72, 1043-1046) (3.00 g, 14.5 mmol, 1 equiv) in phosphorus oxychloride (30 mL) was added diisopropylethylamine (2.00 mL, 11.6 mmol, 0.8 equiv). The mixture was heated to 90° C. for 4.5 hours. After cooling, the mixture was carefully quenched with ice-water and extracted with dichloromethane. The organic extract was washed with saturated aqueous sodium bicarbonate solution, dried over anhydrous sodium sulphate, filtered, and concentrated under vacuum to give a solid. Trituration (diethyl ether) afforded 2.38 g (73%) of ethyl 5-chloropyrazolo[1,5-a]pyrimidine-3-carboxylate as a solid. LCMS (ESI) m+H=226.2 (mono chlorinated isotope pattern); 1H NMR (400 MHz, CDCl3) δ: 8.63 (d, 1H), 8.56 (s, 1H), 6.99 (d, 1H), 4.43 (q, 2H), 1.42 (t, 3H).

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