[CH3:1][O:2][C:3](=[O:21])[CH:4]([C:9]1[C:14]([N+:15]([O-:17])=[O:16])=[CH:13][CH:12]=[CH:11][C:10]=1[N+:18]([O-:20])=[O:19])C(OC)=O.Cl(O)(=O)(=O)=O.C(OCC)(=O)C.CO>C(O)(=O)C>[CH3:1][O:2][C:3](=[O:21])[CH2:4][C:9]1[C:14]([N+:15]([O-:17])=[O:16])=[CH:13][CH:12]=[CH:11][C:10]=1[N+:18]([O-:20])=[O:19]
10.08 g (33.8 mmol) of dimethyl-2-(2,6-dinitrophenyl)-malonate is mixed in 54 ml of glacial acetic acid with 2.7 ml of perchloric acid and refluxed at 125° C. In this case, the ethyl acetate that is produced is distilled off. After 90 minutes, the reaction is brought to a halt, since starting material is no longer present according to TLC. The reaction mixture is poured into ice water and extracted three times with ethyl acetate. The combined organic extracts are shaken with 5% sodium bicarbonate solution, with water and with brine. After the organic phase is dried, the desiccant is filtered off and the solvent is spun off, a residue remains that is chromatographed on silica gel (mobile solvent ethyl acetate/hexane). 4.69 g of the (2,6-dinitrophenyl)-acetic acid, which then is esterified with methanol (16 ml) and concentrated sulfuric acid (0.4 ml), is isolated. To this end, the acid and the reagents are refluxed for seven hours. The methanol is spun off, and the residue is worked up in the usual way. After chromatography on silica gel (mobile solvent ethyl acetate/hexane), 4.43 g (89%) of the desired ester is obtained.
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