合成路线1

Methyl 4-amino-2,5-difluoro-3-methylbenzoate (I) was oxidized to the corresponding nitro derivative (II) with sodium perborate in TFA-AcOH. Acid hydrolysis of the methyl ester afforded carboxylic acid (III), which was converted into acid chloride (IV) employing oxalyl chloride and a catalytic amount of DMF. Condensation of (IV) with the magnesium salt of diethyl malonate, followed by acid-catalyzed decarbethoxylation gave rise to keto ester (V). Subsequent condensation of (V) with triethyl orthoformate in the presence of acetic anhydride yielded the ethoxymethylene derivative (VI). Reaction of (VI) with aniline (VII) followed by cyclization of the intermediate enamine in the presence of K2CO3 afforded quinolone (VIII). The nitro group of (VIII) was then reduced to aniline (IX) by means of iron and AcOH. Finally, acid deprotection of the Boc group of (IX) gave the title compound.