Acetic Anhydride → Ethyl 1-(2,4-difluorophenyl)-6-fluoro-1,4-dihydro-7-methoxy-4-oxo-1,8-naphthyridine-3-carboxylate

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Reaction Steps

In 1 ml of dioxane were dissolved 100 mg of ethyl 2-[2-(2,4-difluorophenylamino)-5-fluoro-6-methoxynicotinoyl]acetate, 55 mg of acetic anhydride and 60 mg of ethyl ortho-formate, and the resulting solution was subjected to reaction under reflux for 7 hours. Subsequently, the reaction mixture was added to a mixture of 3 ml of ethyl acetate and 3 ml of water, and the organic layer was separated, washed successively with 3 ml of water and 3 ml of saturated aqueous sodium chloride solution, and then dried over anhydrous magnesium sulfate. The solvent was removed by distillation under reduced pressure, and to the crystalline material thus obtained was added 1 ml of diethyl ether, after which crystals were collected by filtration to obtain 45 mg (yield 43.8%) of ethyl 1-(2,4-difluorophenyl)-6-fluoro-1,4-dihydro-7-methoxy-4-oxo-1,8-naphthyridine-3-carboxylate. The physical properties of this compound were identical with those of the compound obtained in Example 41.

Provenance & Evidence