1. Synthesis of 1-isoquinolinecarboxaldehyde: 1-methylisoquinoline (300 mg, 2.10 mmol) was dissolved in 1,4-dioxane (20 mL). Selenium dioxide (323 mg, 2.91 mmol) was added to the solution, followed by heating and refluxing under nitrogen protection for 1.5 hours. After completion of the reaction, it was cooled to room temperature and the reaction mixture was filtered through diatomaceous earth. The filtrate was distilled under reduced pressure to remove the solvent. The resulting residue was purified by silica gel column chromatography using n-hexane/ethyl acetate (5:1, v/v) as eluent, and the eluent grades containing the target product were collected, resulting in 1-isoquinolinecarboxaldehyde (252 mg, 77% yield) as a white solid. The structure of the product was confirmed by 1H-NMR (CDCl3) δ: 7.73-7.79 (m, 2H), 7.88-7.93 (m, 2H), 8.74-8.76 (m, 1H), 9.30-9.33 (m, 1H), 10.39 (s, 1H) and MS (ESI) m/z 158 (M++1).
