Anhydrous N,N-dimethylformamide (7.0 mL, 90.4 mmol) was cooled to 5-10°C under nitrogen protection. Triclosan (7.8 mL, 83.7 mmol) was slowly added dropwise to the cooled N,N-dimethylformamide for a controlled period of a few minutes. Subsequently, anhydrous 1,2-dichloroethane (25 mL) was added and methyl 2-pyrrolecarboxylate (9.46 g, 75.6 mmol) was dissolved in another portion of anhydrous 1,2-dichloroethane (25 mL), and this solution was added to the reaction system after cooling it to 0-5°C. The reaction mixture was heated to reflux and maintained for 15 minutes. After completion of the reaction, it was cooled to room temperature and treated with a mixture of ethyl acetate (60 mL) and water (75 mL), then the mixture was poured into saturated sodium bicarbonate solution (350 mL) to separate the organic layer. The aqueous layer was extracted three times with ether, all organic extracts were combined, washed twice sequentially with saturated aqueous sodium carbonate solution, dried over anhydrous sodium sulfate, and the solvent was subsequently evaporated under vacuum. The resulting solid was sublimated at 60 °C under reduced pressure (20~10^-3 Torr) and collected at 3 h intervals to give finally methyl 5-formyl-1H-pyrrole-2-carboxylate (7.79 g, 50.1 mmol, 66% yield). The product was characterized by 1H-NMR (CDCl3): δ 10.57 (broad single peak, 1H), 9.70 (single peak, 1H), 6.95 (multiple peaks, 2H), 3.94 (single peak, 3H).
