[C:1]([O:5][C:6]([NH:8][C:9]1[S:13][C:12]([C:14]([O:16][CH3:17])=[O:15])=[CH:11][C:10]=1[N+:18]([O-])=O)=[O:7])([CH3:4])([CH3:3])[CH3:2].[H][H]>[Pd].CO>[NH2:18][C:10]1[CH:11]=[C:12]([C:14]([O:16][CH3:17])=[O:15])[S:13][C:9]=1[NH:8][C:6]([O:5][C:1]([CH3:2])([CH3:3])[CH3:4])=[O:7]A solution of methyl 5-(tert-butoxycarbonylamino)-4-nitrothiophene-2-carboxylate 88 (0.165 mmol, 50 mg) and palladium on activated carbon (0.083 mmol, 9.79 mg) in methanol (5 mL) was stirred for 1 h at rt with hydrogen gas bubbling through. Additional (0.2 eq) of Pd/C was added and stirred for 1 h. Reaction mixture was filtered and the filtrate was concentrated under reduced pressure to give methyl 4-amino-5-(tert-butoxycarbonylamino)thiophene-2-carboxylate 89 (45 mg, 100%). NMR (400 MHz, CDCl3) 1.52 (s, 9H), 3.83 (s, 3H), 6.85 (br s, 1H), 7.30 (s, 1H). (m/z)=273 (M+H)+.
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