Phosphorus trichloride → 2-Chloro-3-ethoxycarbonyl-6,7-difluoroquinoline

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A mixture of 3-ethoxycarbonyl-6,7-difluoro-1-hydroxy-2-oxoquinoline (25 g at a concentration of 75 mol %, equivalent to 69.65 mmol), 3-ethoxycarbonyl6,7-difluoro-2-oxoquinoline (25 g at a concentration of 5 mol %, equivalent to 4.9 mmol), phosphorus trichloride (59.6 g, equivalent to 433.5 mmol) and phosphoryl chloride (15.05 g, equivalent to 98.05 mmol) in 1,2-dichloroethane (170 cm3) is heated at reflux for 3 hours. After cooling to 0° C., the reaction mixture is poured onto slushed ice (250 g of ice +250 g of water at 0° C.) and left to separate overnight. The organic phase is washed with saturated NaHCO3 solution (100 cm3), followed by water (100 cm3), and then concentrated to dryness in order to obtain 19.8 g of 3-ethoxycarbonyl-6,7-difluoro-2-chloroquinoline of 90% assay (HPLC), equivalent to a yield of 88%.

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