To a solution of 2-tert-butyl-4-fluorophenyl methyl carbonate (1.81 g, 8 mmol) in H2SO4 (98%, 1 mL) was added slowly a cooled mixture of H2SO4 (1 mL) and HNO3 (1 mL) at 0° C. The mixture was stirred for 2 h while warming to room temperature, poured into ice and extracted with diethyl ether. The ether extract was washed with brine, dried over MgSO4 and concentrated. The residue was purified by column chromatography (0-10% EtOAc-Hexane) to give 2-tert-butyl-4-fluoro-5-nitrophenyl methyl carbonate (C-7-a) (1.2 g, 55%) and 2-tert-butyl-4-fluoro-6-nitrophenyl methyl carbonate (C-6-a) (270 mg, 12%). 2-tert-Butyl-4-fluoro-5-nitrophenyl methyl carbonate (C-7-a): 1H NMR (400 MHz, DMSO-d6) δ 8.24 (d, J=7.1 Hz, 1H), 7.55 (d, J=13.4 Hz, 1H), 3.90 (s, 3H), 1.32 (s, 9H). 2-tert-butyl-4-fluoro-6-nitrophenyl methyl carbonate (C-6-a): 1H NMR (400 MHz, DMSO-d6) δ 8.04 (dd, J=7.6, 3.1 Hz, 1H), 7.69 (dd, J=10.1, 3.1 Hz, 1H), 3.91 (s, 3H), 1.35 (s, 9H).
