Phosphorus oxychloride → ethyl 4-chloro-1-ethyl-1H-pyrazolo[3,4-b]pyridine-5-carboxylate

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Reaction Steps

(1-Ethylpyrazol-5-yl-amino)methylenemalonate diethyl ester (10.0 g, 42.6 mmol) was dissolved in 50 mL POCl3. This solution was heated at reflux for 10 h before the POCl3 was removed under reduced pressure. The resulting brown residue was diluted with 5 mL EtOH and extracted with hot hexane (200 mL×3). The combined organic layers were evaporated under reduced pressure to afford the title compounds which formed light green needle shaped crystals upon standing at room temperature (5.4 g, 21.3 mmol, 50% yield). This material is identical to the one obtained in Preparation 3 (1H NMR, 13C NMR, MS, and HPLC).

Provenance & Evidence