[C:1]([NH:4][C:5]1[CH:10]=[CH:9][C:8]([C:11]2[C:12]([C:17]#[N:18])=[C:13]([NH2:16])[O:14][CH:15]=2)=[CH:7][CH:6]=1)(=[O:3])[CH3:2].[C:19]([O:22][CH:23](OCC)OCC)(=O)[CH3:20]>C(O)(=O)C>[C:1]([NH:4][C:5]1[CH:6]=[CH:7][C:8]([C:11]2[C:12]([C:17]#[N:18])=[C:13]([N:16]=[CH:23][O:22][CH2:19][CH3:20])[O:14][CH:15]=2)=[CH:9][CH:10]=1)(=[O:3])[CH3:2]At room temperature, to the mixture of 4-(4-acetamidophenyl)-2-amino-3-cyanofurane 5 (6.0 g, 25 mmol) in acetic acid (60 mL), diethoxymethyl acetate (41 mL, 25 mmol) was added dropwise. The mixture was stirred at room temperature for 30 min and then concentrated (below 40° C. in water bath). The residual paste was dried up with a pump. The dried solid material was triturated with ether then filtrated to afford 6 (3.93 g) as a solid. MS(ES) m/e 298 [M+H].
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