Dimethylformamide → (E)-5-Isopropoxy-1-(2-pyridyl)-2-styryl-1H-benzimidazole oxalate

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Reaction Steps

According to a literature procedure (Sala, T.; Sargent, M. V. J. Chem. Soc. Perkin Trans. I. 1979, 2593.), to a solution of (E)-5-hydroxy-1-(2-pyridyl)-2-styryl-1H-benzimidazole (63.8 mg, 0.2 mmol) in N,N-dimethylformamide (2 ml), potassium carbonate (140 mg, 1.0 mmol) and 2-bromopropane (0.2 ml, 2.0 mmol) was added at room temperature. This resulting mixture was stirred at room temperature for 19 h. To this mixture, ice-cold water (10 ml) was added and the whole was extracted with ethyl acetate and n-hexane (1:1, 2×20 ml). Combined organic layer was washed with water (2×20 ml), brine (20 ml), dried (magnesium sulfate) and filtered. The filtrate was concentrated and the residue was purified by column chromatography (silica gel, 10 g; n-hexane/ethyl acetate (5/1) to afford the desired compound (9.3 mg, 13%); 1H-NMR (CDCl3) δ: 8.78-8.75 (1H, m), 8.01-7.79 (2H, m), 7.54-7.22 (8H, m), 7.14 (1H, d, J=16.11 Hz), 6.99-6.87 (2H, m), 4.65-4.55 (1H, m), 1.39 (6H, d, J=5.9 Hz). The free base and oxalic acid were dissolved into ethyl acetate. Concentration and recrystallization from ethyl acetate/n-hexane yielded the titled compound. MW: 445.48; mp: 165.0-166.0° C.

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