Sodium hydride (60% dispersion in mineral oil, 39 mg, 0.97 mmol) was added portionwise to a stirred solution of 7-nitro-2,3-dihydro-1H-pyrazolo[1,5-a]imidazole (0.125 g, 0.81 mmol) in anhydrous THF (10 mL) at room temperature under a nitrogen atmosphere. The mixture was stirred for 10 min. before a solution of tert-butyl 4-(2-(tosyloxy)ethyl)piperidine-1-carboxylate (0.31 g, 0.81 mmol) in THF (5 mL) was added portionwise over 10 min. The reaction was stirred for 6 hr at room temperature followed by 18 hr at 50° C. Further sodium hydride (60% dispersion in mineral oil, 39 mg, 0.97 mmol) was added and stirring continued at 60° C. for a further 24 h. The reaction was cooled and water was added dropwise. The mixture was extracted with EtOAc and the combined organics were dried over MgSO4 and concentrated under reduced pressure. The crude residue was purified via silica gel chromatography (0-100% EtOAc/isohexane) to give tert-butyl 4-(2-(7-nitro-2,3-dihydro-1H-pyrazolo[1,5-a]imidazol-1-yl)ethyl)piperidine-1-carboxylate as a yellow oil (50 mg, 17%). 1H NMR (400 MHz, CDCl3) δ 7.83 (s, 1H), 4.24-4.16 (m, 2H), 4.25-3.97 (m, 2H), 3.83-3.77 (s, 2H), 3.27 (s, 2H), 3.22 (t, J=6.8 Hz, 2H), 2.72-2.62 (s, 2H), 1.73-1.65 (m, 3H), 1.46-1.44 (m, 9H) 1.40-1.05 (m, 2H)
