Short-RInChIKey=SA-FUHFF-UHFFFADPSC-WJPCYFBJDH-UHFFFADPSC-NUHFF-NUHFF-NUHFF-ZZZ

In a vial, ethyl 3-azido-1-(3,5-difluorobenzyl)-1H-pyrazole-4-carboxylate (50.0 mg, 163 μmol, 1.00 equiv) was dissolved in THF (6.00 mL) and water (6.00 mL) (1:1) and copper;sulfate (5.19 mg, 32.5 μmol, 0.20 equiv), sodium ascorbate (32.2 mg, 163 μmol, 1.00 equiv) and methyl 4-ethynylbenzoate (33.9 mg, 212 μmol, 1.30 equiv) were added. The reaction mixture was stirred at 50 °C for 16 hours. For work up the reaction mixture was diluted in water and extracted three times with methylene chloride. The combined organic phase was washed with water and brine, dried over Na2SO4 and filtered.