General procedure for the synthesis of methyl 5-bromo-3-pyrrolecarboxylate from methyl 3-pyrrolecarboxylate: Referring to the literature method (Example 22, Synthesis of methyl 5-bromo-1H-pyrrole-3-carboxylate); dissolve methyl 1H-pyrrole-3-carboxylate (3.06 g) in tetrahydrofuran (30 mL) and cool to -78°C. Under stirring, N-bromosuccinimide (4.38 g) and pyridine (3 drops) were added sequentially. The reaction mixture was kept stirred at -78 °C for 1 hour. After completion of the reaction, water was added to the mixture and extracted with ethyl acetate. The organic layers were combined and washed sequentially with saturated aqueous sodium bicarbonate, water and saturated saline. The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: hexane/ethyl acetate=5:1) to afford methyl 5-bromo-3-pyrrolecarboxylate (3.08 g, 62% yield) as a pale yellow solid. The structure of the product was confirmed by 1H-NMR (CDCl3): δ 3.81 (3H, s), 6.58 (1H, m), 7.36 (1H, m), 8.60 (1H, brs).
