General procedure for the synthesis of 1-methyl-1H-benzimidazole-5-methanol from ethyl 1-methyl-1H-benzimidazole-5-carboxylate:
Step 1-1-5 (1-methyl-1H-benzimidazol-5-yl) methanol synthesis: lithium aluminum hydride (9.70 g, 256 mmol) was suspended in dry tetrahydrofuran (100 mL) under argon protection. A tetrahydrofuran solution (100 mL) of ethyl 1-methyl-1H-benzimidazole-5-carboxylate (26.1 g, 128 mmol) prepared in step 1-1-4 was added slowly and dropwise under cooling in an ice bath. The reaction mixture was stirred under ice bath cooling for 1 hour. Subsequently, the reaction was quenched by slow addition of saturated sodium bicarbonate solution under ice bath cooling. The solid precipitate was removed by filtration and the filtrate was concentrated. The concentrated residue was dissolved in chloroform, the organic phase was washed with saturated sodium bicarbonate solution and concentrated again. The concentrate was purified by silica gel column chromatography (eluent ratio: chloroform:methanol=10:1 to 5:1) to afford 1-methyl-1H-benzimidazole-5-methanol (11.4 g, 55% yield) as a light red powder.
1H-NMR (CDCl3) δ: 7.85 (s, 1H), 7.77 (s, 1H), 7.37-7.34 (m, 2H), 4.80 (s, 2H), 3.84 (s, 3H), 1.92 (brs, 1H).
Mass spectrum, m/z: 162 (M+), 133 (base).
