Sodium Bicarbonate → 5-(5-azido-4-fluorooxepan-2-yl)-1-methyl-4-nitro-1H-pyrazole

Participants

Reaction Steps

A solution of deoxo-Fluor (50% in THF, 0.576 mL, 1.56 mmol) was added dropwise to an ice-cooled solution of 5-azido-2-(2-methyl-4-nitro-pyrazol-3-yl)oxepan-4-ol (353 mg, 1.25 mmol, intermediate 27) in DCM (6 mL). The mixture was allowed to warm to room temperature whilst stirring for 16 hr before being cooled in an ice bath and saturated aqueous NaHCO3 (10 mL) slowly added. The organic layer was passed through a phase separation cartridge and concentrated under reduced pressure. Purification via silica gel chromatography (0-50% EtOAc/isohexane) gave 5-(5-azido-4-fluorooxepan-2-yl)-1-methyl-4-nitro-1H-pyrazole as a clear gum. To a solution of this gum (145 mg, 0.51 mmol) in THF (5 mL) and water (1 mL) was added triphenylphosphine (147 mg, 0.56 mmol) and the mixture heated at 60° C. for 2 hr. The mixture was diluted with EtOAc (10 mL) and washed with brine (2×5 mL). The organic layer was passed through a phase separation cartridge and concentrated under reduced pressure. The residue was dissolved in DCM (2 mL) and DIPEA (0.178 mL, 1.02 mmol) and di-tert-butyl dicarbonate (134 mg, 0.61 mmol) were added. The mixture was stirred at room temperature for 2 hr. Water (2 mL) was added and the mixture extracted with DCM (3×2 mL). The combined organic layers were passed though a phase separation cartridge, concentrated under reduced pressure and the residue purified via silica gel chromatography (0-50% EtOAc/isohexane) to give tert-butyl N-[5-fluoro-7-(2-methyl-4-nitro-pyrazol-3-yl)oxepan-4-yl]carbamate as a clear gum (180 mg, 39% over three steps). 1H NMR (400 MHz, CDCl3) δ 8.01 (s, 1H), 5.54 (dd, J=10.5, 4.2 Hz, 1H), 5.10-4.92 (m, 2H), 4.21-4.09 (m, 2H), 4.05 (s, 3H), 3.74-3.62 (m, 1H), 2.57-2.38 (m, 1H), 2.35-2.15 (m, 2H), 1.91-1.81 (m, 1H), 1.46 (s, 9H).

Provenance & Evidence