Synthesis
The general procedure for the synthesis of 3-hydroxymethylindazole from indazole-3-carboxylic acid is as follows:
1. Synthesis of (1H-indazol-3-yl)methanol [Compound (I)]: indazole-3-carboxylic acid (500 mg, 3.08 mmol) was dissolved in tetrahydrofuran (THF, 10 mL) and sodium bis(2-methoxyethoxy)aluminum hydride (70% toluene solution, 1.78 g, 6.17 mmol) was added. It was cooled in an ice bath under argon protection and subsequently heated and stirred at reflux for 2 hours.
2. Cooled in an ice bath again, added sodium bis(2-methoxyethoxy)aluminum hydride (70% toluene solution, 2.67 g, 9.25 mmol) to the reaction mixture and continued to heat and reflux for 2 hours.
3. After completion of the reaction, the ice bath was cooled, 2 mol/L sodium hydroxide solution (10 mL) was added and stirred for 15 minutes at room temperature.
4. The organic layer was separated and the aqueous layer was extracted with THF (5 mL × 3). Combine the organic layers and wash with saturated brine.
5. The aqueous layer was then extracted with ethyl acetate (5 mL × 2), all organic layers were combined, dried with anhydrous magnesium sulfate, and concentrated under reduced pressure.
6. The residue was recrystallized with toluene/THF (10:1, 5 mL), the precipitated crystals were collected by filtration and washed with toluene/THF (10:1, 1 mL).
7. The resulting crystals were dried under pressure to give compound (I) (349 mg, 2.36 mmol, 77% yield).
Characterization data:
1H-NMR (DMSO-d6, ppm): δ 4.80 (2H, d, J = 5.5 Hz), 5.19 (1H, br), 7.09 (1H, t, J ≈ 8 Hz), 7.33 (1H, t, J ≈ 8 Hz), 7.48 (1H, d, J = 8.4 Hz), 7.85 (1H, d, J = 8.4 Hz).
13C-NMR (DMSO-d6, ppm): δ 56.7, 109.9, 119.6, 120.5, 121.4, 125.8, 140.9, 145.5.
Mass Spectrometry (C8H9N2O): Calculated [M + H]+: 149.0715, measured: 149.0710 (error: -0.5 mDa).
Melting point: 142-143°C.
References
[1] Patent: EP1878737, 2008, A1. Location in patent: Page/Page column 12
[2] Patent: WO2005/9958, 2005, A1. Location in patent: Page 100-101
[3] Patent: US2006/142247, 2006, A1. Location in patent: Page/Page column 28
[4] Angewandte Chemie - International Edition, 2014, vol. 53, # 28, p. 7259 - 7263
[5] Angew. Chem., 2014, vol. 126, # 28, p. 7387 - 7391,5
