Lithium borohydride → (1-methyl-3-nitro-1H-pyrazol-5-yl)methanol

A 100-mL three-neck round-bottomed flask equipped with a magnetic stirrer, addition funnel and nitrogen inlet was purged with nitrogen and charged with 156b (0.67 g, 3.6 mmol), THF (20 mL) and cooled to 0° C. using an ice bath. 2 M lithium borohydride solution (3.6 mL, 7.2 mmol) was added dropwise at a rate that maintained the internal reaction temperature below 5° C. After the addition was complete, the cooling bath was removed and the reaction was stirred at room temperature for 3 h. The reaction was cooled to 0° C. using an ice bath, and saturated aqueous sodium bicarbonate (30 mL) was added dropwise. The layers were separated, and aqueous layer was extracted with ethyl acetate (3×30 mL). The combined organic layers were washed with brine (30 mL), dried over sodium sulfate and concentrated under reduced pressure. The residue was purified by column chromatography (silica, ethyl acetate/hexanes) to afford a quant. yield (0.56 g) of (1-methyl-3-nitro-1H-pyrazol-5-yl)methanol (156c) as an off-white solid: MS (ESI+) m/z 158.1 (M+H).