Example 2: Synthesis of 3-[(dimethylamino)diazenyl]-4-bromothiophene-2-carboxamide (Compound 2)
Step a: Synthesis of methyl 3-amino-4-bromothiophene-2-carboxylate
To a solution of methyl 3-aminothiophene-2-carboxylate (1 g, 6.36 mmol) in acetic acid (10 mL), a solution of bromine (0.32 mL, 6.36 mmol) in acetic acid (1 mL) was slowly added, and the addition process lasted for 5 min, and the reaction was carried out at room temperature. After addition, the reaction mixture was stirred at the same temperature for 16 hours. After completion of the reaction, the mixture was poured into ice-cold water and extracted with chloroform (3 x 100 mL). The organic layers were combined, washed sequentially with water and brine and dried over anhydrous sodium sulfate. The desiccant was removed by filtration and the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography with the eluent petroleum ether-ethyl acetate (95:5, v/v) to afford the target product methyl 3-amino-4-bromothiophene-2-carboxylate as a light yellow solid (0.5 g, 33% yield) with a melting point of 58-60°C. The residue was extracted with water and sodium sulfate.
1H NMR (400 MHz, CDCl3): δ 7.29 (s, 1H), 5.63 (br s, 2H), 3.85 (s, 3H).
