合成路线1

3,5-Dimethylfluorobenzene (VIII) is treated with chlorine in the presence of anhydrous FeCl3 in either solvent-free conditions or in 1,2-dichloroethane to yield the 2,4-dichlorobenzene derivative (IX). Photochemical chlorination of compound (IX) affords 2,4-dichloro-3-(dichloromethyl)-1-fluoro-5-(trichloromethyl)benzene (X), which is further oxidized with concentrated sulfuric acid at 70 °C to give 2,4-dichloro-5-fluoro-3-formylbenzoic acid (XI) (1, 2). Aldehyde (XI) is next condensed with hydroxylamine hydrochloride (XII) in either an ethanolic NaOH basic media at 60 °C (1, 2) or in formic acid (2) to afford aldoxime (XIII) and the 3-cyanobenzoic acid derivative (XIV), respectively. Treatment of either of the two condensation products (XIII) and (XIV) with refluxing thionyl chloride affords the 3-cyanobenzoyl chloride derivative (XV) (1, 2), which is coupled with ethyl 3-(dimethylamino)acrylate (XVI) by means of DIEA in dichloromethane at 50 °C (1, 2) or triethylamine in toluene at 60-80 °C (3) to produce the 1,3-ketoester (XVII). Tertiary dimethylenamine (XVII) is converted to the secondary cyclopropylenamine (XIX) by treatment with cyclopropylamine (XVIII) in the presence of acetic acid in dichloromethane/water (1, 2) or in a mixture of ethanol/ether (3). Without isolation, intermediate (XIX) undergoes cyclization in the presence of potassium carbonate in N-methylpyrrolidone at 60-70 °C (1, 2) or in acetonitrile (3), affording the ethyl ester (IV). Compound (IV) is hydrolyzed in the presence of sulfuric acid in refluxing AcOH/water to yield the free carboxylic acid (I) (1, 2). Scheme 2.
An alternative pathway for the synthesis of intermediate (XV) proceeds as follows. Friedel-Craft’s acylation of 2,4-dichloro-1-fluorobenzene (XX) with acetyl chloride in the presence of AlCl3 and subsequent oxidation with sodium hypochlorite in 1,4-dioxane gives 2,4-dichloro-5-fluorobenzoic acid (XXI), which is nitrated with HNO3/H2SO4 to give the nitrobenzoic acid (XXII). Esterification of compound (XXII) by means of thionyl chloride in methanol followed by hydrogenation in the presence of Raney-Ni in methanol yields amino ester (XXIII), which is subjected to a Sandmayer reaction with CuCN in the presence of 2-methyl-2-nitropropane (t-BuNO2) in DMF at 60 °C. The intermediate thus obtained is then treated with lithium hydroxide in THF/water and the resulting carboxylic acid is finally chlorinated with thionyl chloride in toluene to afford acyl chloride (XV) (3). Scheme 2.