[CH3:1][N:2]([N:4]=[N:5][C:6]1[CH:10]=[CH:9][S:8][C:7]=1[C:11]([O:13]C)=[O:12])[CH3:3].[OH-].[Na+].Cl>CO.O>[CH3:3][N:2]([N:4]=[N:5][C:6]1[CH:10]=[CH:9][S:8][C:7]=1[C:11]([OH:13])=[O:12])[CH3:1]To a solution of methyl 3-[(dimethylamino)diazenyl]thiophene-2-carboxylate (200 mg, 0.93 mmol) in methanol (10 mL) was added a solution of sodium hydroxide (93 mg, 2.3 mmol) in water (2 mL) and stirred at rt for 2 h. The mixture was diluted with ice cold water and acidified with dil. HCl and extracted with chloroform. The combined chloroform layer was washed with water, brine and dried over sodium sulfate. The solution was filtered and evaporated the solvent. The residue was chromatographed over silica gel column using hexane-ethyl acetate (80:20) as eluents to give the product as an off-white solid (70 mg, 38%), mp 108-110° C. IR (neat) νmax 3402, 3082, 2923, 1708, 1218, 1116, 1066, 1016, 880, 773 cm−1; 1H NMR (400 MHz, CDCl3): δ 12.21 (1H, s), 7.47 (1H, d, J=5.2 Hz), 7.30 (1H, d, J=5.2 Hz), 3.65 (3H, s), 3.28 (3H, s); LC-MS (positive ion mode): m/z 200 (M+H)+.
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