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) was refluxed for 3 hours and then was stirred at room temperature overnight. The POCl3 was removed by distillation, and the residue was poured into ice-water. The solution was neutralized with 35% NaOH and extracted with CH2Cl2 (4×). The organic layer was separated, washed with water, then brine and then was dried over MgSO4. The solvent was concentrated in vacuo and the residue was 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 was run as described above and then was worked up by neutralization with concentrated NH4OH to a pH of 8 and then the product, which crystallized directly from the solution, was collected by filtration.

Provenance & Evidence