[C:1](Cl)(=[O:5])[CH:2]([CH3:4])[CH3:3].[CH3:7][O:8][C:9]([C:11]1[CH:15]=[C:14]([CH3:16])[S:13][C:12]=1[NH2:17])=[O:10].O>CN(C)P(N(C)C)(N(C)C)=O>[C:9]([C:11]1[CH:15]=[C:14]([CH3:16])[S:13][C:12]=1[NH:17][C:1](=[O:5])[CH:2]([CH3:4])[CH3:3])([O:8][CH3:7])=[O:10]isoButyryl chloride (22.4 g) was added dropwise during 40 minutes to a stirred solution of methyl-2-amino-5-methyl-3-thiophenecarboxylate (34.2 g, 0.2 mol) in dry hexamethylphosphoramide (100 ml) kept at 5°-10° C. This temperature was maintained for a further 1 hour and then the reaction was kept at room temperature for 16 hours. The reaction mixture was poured into water (1600 ml) and the yellow precipitate was filtered off, washed with water and dried at 50° C. Recrystallization of the solid from petroleum ether (b.p. 60°-80° C. yielded cream crystals (39.6 g, 88%), m.p. 63°-65° C.
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