Tert-butyl 4-(3-methoxy-4-nitrophenyl)piperazine-1-carboxylate → Tert-butyl 4-(4-amino-3-methoxyphenyl)piperazine-1-carboxylate

A solution of 1-tert-butyl 1-piperazinecarboxylate (Sigma Aldrich, 3.37 g, 18.12 mmol), 5-fluoro-2-nitroanisole (Oakwood Products, West Columbia, S.C., 3.10 g, 18.12 mmol) and N-ethyl-N-isopropylpropan-2-amine (6.31 mL, 36.2 mmol) in DMSO (11 mL) in a 20 mL glass microwave tube was sealed and heated in a heating block at 95° C. overnight (20 h). Upon cooling, the reaction mixture crystallized to a yellow solid. It was diluted with 150 mL of EtOAc, washed sequentially with 20 mL of water, 20 mL of NaHCO3 and brine (20 mL). The organic solution was dried over MgSO4 and concentrated affording tert-butyl 4-(3-methoxy-4-nitrophenyl)piperazine-1-carboxylate (6.14 g, 18.20 mmol, 99% yield) as a yellow crystalline solid. m/z (ESI, +ve ion) 359.9 (M+Na)+. 1H NMR (400 MHz, MeOH-d4) δ ppm 7.96 (1H, d, J=9.2 Hz), 6.59 (1H, dd, J=9.4, 2.5 Hz), 6.55 (1H, d, J=2.3 Hz), 3.97 (3H, s), 3.56-3.65 (4H, 3.45-3.52 (4H, m), 1.51 (9H, s). Pd/C (10 wt. %, dry basis, wet activated, 284 mm, 0.267 mmol) and tert-butyl 4-(3-methoxy-4-nitrophenyl)piperazine-1-carboxylate (600 mg, 1.78 mmol) were treated with EtOH (30 mL) and allowed to stir under an atmosphere of hydrogen (balloon) for 23 h. The reaction mixture was filtered through an acrodisc (0.20 um), the resulting purple solution was then concentrated on the rotovap and then under vacuum overnight affording tert-butyl 4-(4-amino-3-methoxyphenyl)piperazine-1-carboxylate (539 mg, 1.76 mmol, 99% yield) as a purple film. m/z (ESI, +ve ion) 307.0/309.0 (M+H)+. 1H NMR (400 MHz, MeOH) δ ppm 6.71 (1H, d, J=8.4 Hz), 6.62 (1H, d, J=2.3 Hz), 6.46 (1H, dd, J=8.3, 2.4 Hz), 3.85 (3H, s), 3.51-3.61 (4H, m), 2.92-3.02 (4H, m), 1.47-1.52 (9H, s).