Formaldehyde → 6,6-difluoro-N,N-dimethyl-1-(1-methyl-4-nitro-1H-pyrazol-5-yl)azepan-4-amine

To a solution of tert-butyl 6,6-difluoro-1-(1-methyl-4-nitro-1H-pyrazol-5-yl)azepan-4-ylcarbamate (0.96 g, 2.56 mmol) in MeOH (3 mL) was added HCl in 1,4-dioxane (4 M, 12.8 mL, 51.2 mmol) and the solution was stirred at room temperature for 16 hr. The solvents were removed under reduced pressure and the residue was dissolved in DCM (30 mL). The organic layer was washed with saturated aqueous NaHCO3 solution (30 mL), dried over Na2SO4 and the solvent removed under reduced pressure to give 6,6-difluoro-1-(1-methyl-4-nitro-1H-pyrazol-5-yl)azepan-4-amine. This amine was dissolved in MeOH/THF (1:1, 50 mL) and treated with formaldehyde (38% in water, 0.45 mL, 6.21 mmol). After 5 min, sodium cyanoborohydride (0.39 g, 6.21 mmol) was added portionwise and the resulting mixture stirred for 5 hr. Additional formaldehyde (38% in water, 0.45 mL, 6.21 mmol) and sodium cyanoborohydride (0.39 g, 6.21 mmol) were added and the resulting mixture was stirred for 60 hr. The solvents were removed under reduced pressure and the crude was purified via silica gel column chromatography (0-10% MeOH/DCM) to give 6,6-difluoro-N,N-dimethyl-1-(1-methyl-4-nitro-1H-pyrazol-5-yl)azepan-4-amine as a yellow oil (0.64 g, 82% over two steps). 1H NMR (400 MHz, CDCl3) δ 8.07-8.03 (m, 1H), 3.82 (s, 3H), 3.70-3.57 (m, 2H), 3.42-3.29 (m, 1H), 3.24-3.05 (m, 1H), 3.04-2.98 (m, 1H), 2.51-2.40 (m, 1H), 2.35-2.29 (m, 6H), 2.20-2.01 (m, 2H), 1.97-1.82 (m, 1H).