合成路线1

The reaction of 3,4-difluoroaniline (I) with carbon disulfide and triethylamine gives triethylammonium N-(3,4-difluorophenyl)dithiocarbamate (II), which by reaction with ethyl chloroformate and triethylamine in chloroform is converted into 3,4-difluorophenyl isothiocyanate (III). The reaction of (III) with diethyl malonate and KOH in dioxane affords the potassium salt (IV), which is treated with chloromethyl methyl ether in DMF to give the corresponding methoxymethylsulfanyl compound (V). The cyclization of (V) at 240 C in diphenyl ether affords 6,7-difluoro-4-hydroxy-2-(methoxymethylsulfanyl)quinoline-3-carboxylic acid ethyl ester (VI), which by treatment with HCl in ethanol gives the corresponding mercapto compound (VII). The cyclization of (VII) with 1,1-dibromoethane by means of K2CO3 and KI in hot DMF yields 5,6-difluoro-1-methyl-4-oxo-4H-[1,3]thiazeto[3,2-a]quinoline-3-carboxylic acid ethyl ester (VIII), which is condensed with piperazine (IX) in DMF to afford the corresponding piperazino-derivative (X). The hydrolysis of (X) with KOH in hot tert-butanol gives the corresponding free acid (XI) , which is finally condensed with 4-(bromomethyl)-5-methyl-1,3-dioxol-2-one (XII) by means of KHCO3 in DMF.