Synthesis
General method: n-Butyllithium (2.5 M hexane solution, 300 μL, 0.72 mmol) was added slowly and dropwise to a solution of anhydrous THF (1.5 mL) of 5-bromoquinoline (100 mg, 0.48 mmol) at -78°C. The reaction solution turned red immediately. The reaction solution immediately turned red, followed by the addition of N,N-dimethylformamide (192 μL, 2.49 mmol). After maintaining the reaction temperature at -78 °C with stirring for 10 min, the reaction was quenched with deionized water (6 mL). The reaction mixture was poured into saturated aqueous sodium bicarbonate solution (10 mL) and extracted with ethyl acetate (3 × 10 mL). The organic layers were combined, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: n-hexane solution of 10% ethyl acetate) to give 5-quinolinecarboxaldehyde as a yellow solid in 53% yield.
