Phosphorus oxychloride → 1-ethyl-4-chloro-1H-pyrazolo[3,4-b]quinoline

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Reaction Steps

A mixture of N-(1-ethylpyrazol-5-yl)anthranilic acid (21.4 g, 0.0925 mol) and phosphorous oxychloride (312.8 g, 2.04 mol) is refluxed for 3 hours and then is stirred at room temperature overnight. The POCl3 is removed by distillation, and the residue is poured into ice water. The solution is neutralized with 35% NaOH and extracted with CH2Cl2 (4×). The organic layer is separated, washed with water, then brine and then is dried over MgSO4. The solvent is concentrated in vacuo and the residue is purified by column chromatography on silica gel eluting with CH2Cl2 to afford 17.5 g (81.7%) of 4-chloro-1-ethyl-1H-pyrazolo[3,4-b]quinoline. Alternatively, the reaction is run as described above, and then is worked up by neutralization with concentrated NH4OH to a pH of 8. Then the product, which crystallized directly from the solution, is collected by filtration.

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