Boron tribromide → 1-Ethyl-8-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-8-fluoro-6,7-dimethoxy-4-oxo-1,4-dihydroquinoline-3-carboxylate (24 g, 74.2 mmol) in Dichloromethane (DCM) (300 mL) was added boron tribromide (35.1 mL, 371 mmol) at −78° C. The mixture was warmed up to rt and stirred at 25° C. overnight. LCMS indicated completion of the reaction. The mixture was diluted with EtOH and concentrated in vacuo. The same procedure was repeated several times to afford 1-ethyl-8-fluoro-6,7-dihydroxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (18 g, 67.4 mmol, 91% yield) as a yellow solid. This product was used in next step reaction without further purification. LCMS (M+H)+: 268.0.

Provenance & Evidence