To 2-ethyl-1-[1-(4-methoxybenzyl)-1H-pyrazol-5-yl]butan-1-ol (1.21 g, 4.20 mmol) in THF (40 mL) at 0° C. was added triphenylphosphine (1.65 g, 6.29 mmol), diethyl azodicarboxylate (1.0 mL, 6.3 mmol), and diphenylphosphoryl azide (1.4 mL, 6.3 mmol). The reaction mixture was warmed to room temperature and stirred for 15.5 h. The solvent was removed in vacuo and the resulting residue was purified by column chromatography (EtOAc/hexanes, 1:9, then 1:4) to give 0.862 g (66%) of 5-(1-azido-2-ethylbutyl)-1-(4-methoxybenzyl)-1H-pyrazole.
