Diethyl (ethoxymethylene)malonate → Diethyl (7,8-difluoro-3-methyl-3,4-dihydro-2H-[1,4]benzoxazine-4-yl)methylenemalonate

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Reaction Steps

To 1.13 g of (-)-7,8-difluoro-2,3-dihydro-3-methyl-4H-[1,4]benzoxazine was added 1.58 g of diethyl ethoxymethylenemalonate, and the mixture was stirred at 130° to 140° C. for 70 minutes. The reaction mixture was subjected as such to column chromatography using 50 g of silica gel and eluted with chloroform to obtain 2.47 g of diethyl [(-)-7,8-difluoro-3-methyl-2,3-dihydro-4H-[1,4]benzoxazin-4- yl]methylenemalonate. This product was dissolved in 5 ml of acetic anhydride, and 10 ml of a mixture of acetic anhydride and concentrated sulfuric acid (2/1 by volume) with stirring under ice-cooling, followed by stirring at 50° to 60° C. for 40 minutes. To the reaction mixture were added ice and an aqueous solution of sodium bicarbonate, and the reaction product was extracted three times with 150 ml portions of chloroform. The combined extract was washed with water, dried over anhydrous sodium sulfate and concentrated under reduced pressure. When a solid began to precipitate, a small amount of diethyl ether was added thereto, and the precipitate was collected by filtration. The precipitate was washed with a small amount of diethyl ether to yield 1.32 g of (-)-ethyl 9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de][1,4]benzoxazine-6-carboxylate.

Provenance & Evidence