2.1.1 Synthesis of 5-bromo-2-thiophenecarboxaldehyde
Under nitrogen protection, 2-thiophenecarboxaldehyde (6.0 g, 53.5 mmol) was dissolved in anhydrous chloroform (125 mL). Subsequently, N-bromosuccinimide (10.4 g, 58.9 mmol) was slowly added and the reaction mixture was stirred for 12 h at room temperature. After completion of the reaction, the mixture was extracted with chloroform (3 × 50 mL), and the organic phases were combined and washed with deionized water (2 × 50 mL). The organic layer was dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography using chloroform as eluent to afford 5-bromo-2-thiophenecarboxaldehyde as a colorless oil (10.0 g, 98% yield).
1H NMR (400 MHz, CDCl3): δ 7.20 (d, 1H, J = 4.0 Hz), 7.53 (d, 1H, J = 8.0 Hz), 9.79 (s, 1H).
