Boron trifluoride etherate → 3,4-Dihydro4-(2-dimethylaminoethyl)-6-nitro-2H-1,4-benzoxazine

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Reaction Steps

Boron trifluoride etherate (2 ml, 16.2 mmol) was added dropwise to a suspension of sodium borohydride (0.46 g, 12 mmol) in dry THF (30 ml) at 0° C., under argon. After 1 hr, a solution of 4-(2- dimethylaminoethyl)-6-nitro-2H-1,4-benzoxazine-3(4H )-one (D1, 1.08 g, 4 mmol) in dry THF (20 ml) was added. The reaction mixture was heated under reflux for 2 hr, then cooled in ice. Aqueous NaHCO3 was added dropwise until effervescence ceased, then the solvent was removed under reduced pressure and the residue dissolved in a mixture of EtOH (10 ml) and 5N HCl (10 ml) and heated under reflux for 45 minutes. After cooling, the solvent was removed under reduced pressure. The residue was treated with satturated K2CO3 solution to pH 8, then extracted with EtOAc. The combined extracts were dried (Na2SO4) and evaporated under reduced pressure to give the title compound (0.94 g, 92%).

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