[NH:1]1[CH:5]=[C:4]([CH:6]=[O:7])[N:3]=[CH:2]1.[H-].[Na+].[CH3:10][CH2:11][CH2:12]Br.C1OCCOCCOCCOCCOCCOC1.[Cl-].[NH4+]>O1CCCC1>[CH2:10]([N:1]1[CH:5]=[C:4]([CH:6]=[O:7])[N:3]=[CH:2]1)[CH2:11][CH3:12]Imidazole-4-carboxaldehyde (30 g, 0.31 mol) was added portionwise to a solution of sodium hydride (13.9 g, 60% dispersion in mineral oil, 0.348 mol) in tetrahydrofuran (450 ml), and the solution was stirred for 45 minutes. n-Propyl bromide (31.2 ml, 0.344 mol) was then added portionwise, followed by 18-crown-6 (150 mg), and the mixture was heated under reflux for 18 hours. Aqueous ammonium chloride solution was added to the cooled solution, and the mixture was extracted with ethyl acetate (2×) and dichloromethane (2×). The combined organic extracts were dried (MgSO4), filtered, and concentrated under reduced pressure. The crude product was purified by column chromatography on silica gel, eluting with ethyl acetate: pentane (40:60), to give the title compound, 20.2 g, 47% yield. 1H-NMR (DMSO-d6, 400 MHz) δ: 0.80 (t, 3H), 1.76 (m, 2H), 3.98 (t, 2H), 7.84 (s, 1H), 8.04 (s, 1H), 9.70 (s, 1H). LRMS: m/z (TSP+) 277.3 [2M+H]+
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