N#N.[CH3:3][O:4][C:5](=[O:21])[CH2:6][C:7]1[S:8][C:9]([C:12]2[CH:17]=[CH:16][CH:15]=[C:14]([N+:18]([O-])=O)[CH:13]=2)=[CH:10][CH:11]=1>CO.[Pd]>[CH3:3][O:4][C:5](=[O:21])[CH2:6][C:7]1[S:8][C:9]([C:12]2[CH:17]=[CH:16][CH:15]=[C:14]([NH2:18])[CH:13]=2)=[CH:10][CH:11]=1(The following reaction is done in an N2 atmosphere.) Dissolve [5-(3-Nitro-phenyl)-thiophen-2-yl]-acetic acid methyl ester (56) (3.15 mg, 11.35 mmol) in MeOH (225 mL) and add Pd on carbon (10% (w/w) Pd content, 1.20 g, 1.13 mmol) followed by NH4CO2H (7.15 g, 113.4 mmol) at rt. Degas the reaction mixture carefully (flush with N2) and stir it for 22 h at rt. Filtrate reaction mixture through a short pad of celite and remove solvent. Purify the obtained crude product by preparative radial chromatography (silica gel, EtOAc/CyH 1+3) to obtain [5-(3-Amino-phenyl)-thiophen-2-yl]-acetic acid methyl ester (57) (2.08 g, 74%) as a yellow solid. 1H NMR (400 MHz, CDCl3): 3.73 (s, 3H); 3.81 (s, 2H); 6.59 (dd, 1H, J1=7.8 Hz, J2=2.0 Hz); 6.86 (br.d, 1H, J=3.5 Hz); 6.88 (t, 1H, J=1.9 Hz); 6.97 (br.d, 1H, J=7.6 Hz); 7.09 (d, 1H, J=3.5 Hz); 7.13 (t, 1H, J=7.7 Hz).
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