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39856-98-9

Example 4-5 Preparation of Compound 4-L: To a solution of 3-bromobenzo[b]thiophene (4-K) (4 g, 18.7 mmol) in ether (Et2O, 20 mL) was slowly added tert-butyllithium (t-BuLi, 15.6 mL, 1.3 M hexane solution) at -78°C. The reaction mixture was kept stirred at -78 °C for 30 min, followed by the addition of N,N-dimethylformamide (DMF, 1.5 g, 20.6 mmol). The cooling bath was removed and the reaction mixture was allowed to gradually warm up to room temperature and continued stirring for 30 min. The mixture was again cooled to -30 °C and another portion of tert-butyllithium (15.6 mL, 1.3 M hexane solution) was added at this temperature. The cooling bath was removed and the mixture was warmed to room temperature and stirred for 30 minutes. Subsequently, the reaction mixture was cooled to -78 °C and a hexane solution of bromine (Br2, 3.9 g, 24.4 mmol) was slowly added. The temperature of the reaction was controlled to gradually increase to 0 °C over 2 hours. After completion of the reaction, the reaction mixture was diluted with 1 M hydrochloric acid (HCl) and extracted with ethyl acetate (EA). The organic phases were combined, concentrated and the residue was purified by silica gel column chromatography to finally obtain 2-bromobenzo[b]thiophene-3-carbaldehyde (4-L) (0.3 g, 7% yield).