[NH2:1][C:2]1[S:14][C:5]2[CH2:6][N:7]([C:9]([O:11][CH2:12][CH3:13])=[O:10])[CH2:8][C:4]=2[C:3]=1[C:15]([O:17]CC)=O.C([O-])=O.[NH4+].[CH:24]([NH2:26])=O>O>[O:17]=[C:15]1[NH:26][CH:24]=[N:1][C:2]2[S:14][C:5]3[CH2:6][N:7]([C:9]([O:11][CH2:12][CH3:13])=[O:10])[CH2:8][C:4]=3[C:3]1=2Diethyl 2-amino-4,6-dihydro-5H-thieno[2,3-c]pyrrole-3,5-dicarboxylate from Example 19A (3.60 g, 12.7 mmol) was dissolved in formamide (72 mL), and ammonium formiate (2.11 g, 20.3 mmol) was added. The mixture was heated to 140° C. overnight, then diluted with water and extracted with ethyl acetate. The organic layer was dried over sodium sulfate, and the solvent was removed in vacuo. The precipitate in the aqueous layer was collected by suction filtration and combined with the organic extracts. The product was purified by column chromatography on silica gel (eluent: DCM/MeOH 100:3) and subsequently triturated with tert-butyl methyl ether to yield 1.74 g (52%) of the title compound.
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