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

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Reaction Steps

A mixture of 23.5 g. 1-ethyl-4-hydroxy-1H-pyrazolo[3,4-b]pyridine- 5-carboxylic acid ethyl ester (0.1 mol.) and 150 ml. of phosphorous oxychloride is refluxed for 4 hours. Subsequently, the excess phosphorous oxychloride is removed by means of vacuum distillation. As soon as the phosphorous oxychloride has been removed, the oily residue solidifies on cooling. It is treated with water and filtered under suction (24.5 g., m.p. 55°-60°). The 4-chloro compound is recrystallized from N-hexane (22.5 g. (87%), m.p. 62°).

Provenance & Evidence