24424-99-5

35344-95-7

821767-61-7

Step A: Di-tert-butyl dicarbonate (Boc2O, 2183 mg, 10.0 mmol) was slowly added to a stirring solution of 1H-pyrazole-4-carboxaldehyde (961 mg, 10.0 mmol) acetonitrile (30 mL) at room temperature, followed by the addition of 4-dimethylaminopyridine (DMAP, 61.1 mg, 0.500 mmol) as a catalyst. The reaction mixture was stirred at room temperature overnight. After completion of the reaction, the mixture was concentrated to dryness under reduced pressure. The residue was extracted by partitioning with ethyl acetate (30 mL) and water (30 mL). The organic phase was separated and washed sequentially with 0.5 N HCl (30 mL) and saturated saline (30 mL). The organic phase was dried over anhydrous magnesium sulfate (MgSO4), filtered and concentrated to give the crude product. The crude product was purified by chromatography on a Biotage 40M silica gel column using hexane/ethyl acetate (4:1, v/v) as eluent. Fractions containing the target product were collected, combined and concentrated under reduced pressure to afford tert-butyl 4-formyl-1H-pyrazole-1-carboxylate (1.4 g, 71% yield) as a solid.