Synthesis of 1H-indazole-1,4-carboxaldehyde (12i): 4-(Hydroxymethyl)-1H-indazole (54 mg, 0.36 mmol) was dissolved in 3 mL of tetrahydrofuran (THF) followed by addition of Dess-Martin periodinane (247 mg, 0.58 mmol). The reaction mixture was stirred overnight at room temperature and quenched with 2.0 M sodium thiosulfate (Na2S2O3) solution upon completion of the reaction. The reaction mixture was extracted with ethyl acetate, the organic layers were combined, washed sequentially with saturated sodium bicarbonate (NaHCO3) solution and brine, and dried over anhydrous magnesium sulfate (MgSO4). The solvent was removed by concentration under reduced pressure and the residue was purified by column chromatography (75% ethyl acetate/hexane) to afford 1-hydro-indazole-4-carbaldehyde (37 mg, 70% yield) as a white solid. Determination by mass spectrometry (electrospray ionization): expected value of M+H = 147.1, measured value = 147.2.
