[NH:1]([C:3]([NH:5][C:6]1[S:10][C:9]([C:11]([O:13][CH2:14][CH3:15])=[O:12])=[C:8]([CH3:16])[CH:7]=1)=[O:4])[NH2:2].[CH:17](OC)(OC)OC.O.C1(C)C=CC(S(O)(=O)=O)=CC=1>C(O)C>[CH3:16][C:8]1[CH:7]=[C:6]([N:5]2[C:3](=[O:4])[NH:1][N:2]=[CH:17]2)[S:10][C:9]=1[C:11]([O:13][CH2:14][CH3:15])=[O:12]A mixture of ethyl 5-(hydrazinecarboxamido)-3-methylthiophene-2-carboxylate (12.80 g, 52.61 mmol), trimethyl orthoformate (6.33 mL, 57.86 mmol) and p-toluenesulfonic acid monohydrate (0.260 g, 1.367 mmol) in ethanol (130 mL) was stirred at reflux for 30 minutes. The reaction mixture was allowed to cool to ambient temperature, and kept at +5° C. for 16 h. The resulting solid was filtered and washed with ethyl acetate. The filtrate was concentrated, and the residue was triturated with ethanol. The combined material was dried to afford the title compound as a cream solid in 70% yield (9.37 g): 1H NMR (300 MHz, DMSO-d6) δ 12.35 (s, 1H), 8.66 (s, 1H), 7.27 (s, 1H), 4.25 (q, J=7.1 Hz, 2H), 2.47 (s, 3H), 1.29 (t, J=7.1 Hz, 3H); MS (ES+) m/z 254.2 (M+1).
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