N-bromobutanimide → methyl 5-(bromomethyl)-1-methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazole-4-carboxylate

Participants

Reaction Steps

Methyl 1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazole-4-carboxylate (7.82 g, 31.8 mmol) was dissolved in CHCl3 (150 ml) and n-bromosuccimide (6.91 g, 38.8 mmol) was added. The reaction was stirred at room temperature, and after 1.5 hours, more NBS (6.23 g, 35.2 mmol) was added. After another hour of stirring, the reaction was filtered, and the solid was washed with chloroform. The filtrate was concentrated, treated with dichlormethane, and refiltered. The filtrate was again concentrated, and filtered through silica gel (˜3 inches, dichlormethane/MeOH). The fractions with product collected, concentrated, and purified on silica gel (dichlormethane/MeOH) to give the desired methyl 5-(bromomethyl)-1-methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazole-4-carboxylate (4.11 g, 82% purity, 10.4 mmol, 33% yield). MS (ESI pos. ion) m/z: 325, 327 (MH+). Calc'd exact mass for C13H13Br79.0N2O3: 324. Calc'd exact mass for C13H13Br81.0N2O3: 326.

Provenance & Evidence