[[(1-Ethyl-3-methyl-5-pyrazolyl)amino]methylene]malonic acid diethyl ester → 1-ethyl-4-hydroxy-3-methyl-1H-pyrazolo[3,4-b]pyridine-5-carboxylic acid ethyl ester

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Reaction Steps

14.8 g of [[(1-ethyl-3-methyl-5-pyrazolyl)amino]methylene]malonic acid diethyl ester (0.05 mol) is dissolved in 50 g of diphenyl ether. The reaction mixture is heated to 235°-250° (bath temperature) and allowed to react at this temperature for 1 to 2 hours, while continuously distilling off the resulting ethanol. The last part of the alcohol is removed by means of a water aspirator. The diphenyl ether is separated by distillation with a fractionation column in vacuo. The 1-ethyl-4-hydroxy-3-methyl-1H-pyrazolo[3,4-b]pyridine-5-carboxylic acid ethyl ester is obtained at b.p.0.1-0.5 125°-129°, yield 10.7 g = 86% of theory, m.p. 91-93°. The compound is recrystallized from ligroin (90°-100°), and has a melting point of 93°-94°. Hydrolysis of this product with aqueous sodium hydroxide yields 1-ethyl-4-hydroxy-3-methyl-1H-pyrazolo[3,4-b]pyridine-5-carboxylic acid, m.p. 212°-213°.

Provenance & Evidence