Acetic Acid → 4,5-Difluoro-2,3-dihydro-1-methyl-7-oxo-1H,7H-pyrido[3,2,1-ij]cinnoline-8-carboxylic acid

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Reaction Steps

29.1 g of methyl ester (6) obtained in Example 2 (1) was added to 80 ml of concentrated hydrochloric acid and 320 ml of acetic acid, and the solution was heated under reflux for 3.5 hours. After air-cooled, 500 ml of water was added to the solution, and the solid was filtered off and washed consecutively with water, ethanol and ether to obtain 23.2 g of crude solid. The obtained crude solid was recrystallized from ethanol and chloroform to obtain 21 g of subject compound (8) in a 80% yield. The result of the analysis of this compound was as follows.

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