GENERAL METHOD: 2-chloro-5-methylthiophene (200 mmol) was dissolved in anhydrous DMF (43.86 g, 600 mmol) under anhydrous conditions, cooled in an ice-water bath and stirred. POCl3 (46.00 g, 300 mmol) was slowly added dropwise. After the dropwise addition was completed, the reaction mixture was continued to be stirred at the temperature of the ice-water bath for 30 min, and then warmed up to 100 °C for 5 h. The reaction was carried out at the temperature of the ice-water bath. Upon completion of the reaction, the mixture was cooled to room temperature and carefully poured into ice water (300 mL). The aqueous phase was extracted with dichloromethane (300 mL × 3) and the organic phase was combined. The organic phase was washed sequentially with 5% brine (200 mL), 10% aqueous K2CO3 (200 mL), and 5% brine (200 mL), and then dried with anhydrous Na2SO4. The solvent was evaporated under reduced pressure to obtain the crude product. Purification of the crude product by column chromatography afforded the target compound 5-chlorothiophene-2-carbaldehyde (10ha): a colorless oil in 22.00 g (75%) yield.1H-NMR (DMSO-d6, 400 MHz) δ: 9.82 (s, 1H), 7.95 (d, J = 4.0 Hz, 1H), 7.39 (d, J = 4.0 Hz, 1H). The obtained 1H-NMR data are in agreement with literature reports [53].
