Water → Ethyl 1-(2,4-difluorophenyl)-7-ethylsulfinyl-6-fluoro-1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxylate

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Reaction Steps

In 10 ml of methylene chloride was dissolved 1.00 g of ethyl 1-(2,4-difluorophenyl)-7-ethylthio-6-fluoro-1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxylate, and 580 mg of m-chloroperbenzoic acid (purity: 80%) was added thereto, after which the resulting mixture was subjected to reaction with ice-cooling for 5 hours. The precipitates were removed by filtration, and to the filtrate thus obtained was added 10 ml of water, after which the pH thereof was adjusted to 7.5 with saturated aqueous sodium hydrogencarbonate solution. The organic layer was thereafter separated, washed with 10 ml of water, and then dried over anhydrous magnesium sulfate. The solvent was removed by distillation under reduced pressure, and the residue thus obtained was purified by a column chromatography [Wako Silica Gel C-200, eluant: toluene-ethyl acetate (10:1 by volume)] to obtain 810 mg (yield 77.9%) of ethyl 1-(2,4-difluorophenyl)-7-ethylsulfinyl-6-fluoro-1,4-dihydro-4-oxo-1,8-naphthyridine-3-carboxylate having a melting point of 150°-151° C. The physical properties of this compound were identical with those of the compound obtained in Example 44.

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