Boron tribromide → 1-Ethyl-5-fluoro-6,7-dihydroxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid

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Reaction Steps

To a solution of ethyl 1-ethyl-5-fluoro-6,7-dimethoxy-4-oxo-1,4-dihydroquinoline-3-carboxylate (65 g, 201 mmol) in Dichloromethane (DCM) (300 mL) was added BBr3 (95 mL, 1005 mmol) at −78° C. The mixture was allowed to warm up to rt, and stirred at 25° C. overnight. LCMS indicated completion of the reaction. The mixture was diluted with MeOH and concentrated to dryness. The same process was repeated several times to afford 1-ethyl-5-fluoro-6,7-dihydroxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (48 g, 180 mmol, 89% yield) as yellow solid. The crude product was a mixture of acid and small amount of methyl ester, which was used in next step reaction without further purification. LCMS: (M+H)+: 268.0.

Provenance & Evidence