Water → HCID 90092931, compound

Participants

Reaction Steps

Under a nitrogen atmosphere, sodium borohydride (0.51 g, 13.60 mmol) was added portionwise to a solution of 3-(thiophen-2-yl)-1H-pyrazole-5-carbaldehyde (34b) (2.02 g, 11.33 mmol) in anhydrous methanol (80 mL). The reaction mixture was stirred at room temperature for 4 hours. Water was added (50 mL) and the mixture was concentrated in vacuo. The residue was dissolved in ethyl acetate (40 mL) and successively washed with water (40 mL) and brine (40 mL). The organic layer was dried over sodium sulfate and concentrated in vacuo. The residue was dissolved in acetonitrile (100 mL) and N-bromosuccinimide (1.35 g, 7.59 mmol) was added. The mixture was stirred for 60 minutes at room temperature, then concentrated in vacuo. The residue was dissolved in ethyl acetate (40 mL) and washed with brine (40 mL). The organic layer was dried over sodium sulfate and concentrated in vacuo. The residue was dissolved in a mixture of chloroform (14 mL) and N,N-dimethylformamide (28 mL). Manganese dioxide (3.74 g, 43.02 mmol) was added and the mixture was stirred at 50° C. for 1 hour. The mixture was filtered through a pad of Celite®, rinced with N,N-dimethylformamide, the filtrate was concentrated in vacuo, and co-evaporated with toluene. The residue was triturated with diethyl ether and filtered to provide 4-bromo-3-(thiophen-2-yl)-1H-pyrazole-5-carbaldehyde (34c) (1.07 g, 4.16 mmol, 37%).

Provenance & Evidence