2-Bromo-4-fluorobenzenesulfonyl chloride (0.631 g) was added to a solution of methyl 7-amino-10H-9-oxa-1,2-diazaphenanthrene-8-carboxylate (Intermediate 6, 0.395 g) in pyridine (20 mL) and DCM (20 mL) and the mixture was allowed to stand at room temperature for 4 days. The resulting solution was evaporated in vacuo, and the residue was partitioned between a mixture of DCM and water and filtered through a phase separator. The filtrate was evaporated to dryness, and the residue was azeotroped with toluene. The residue was purified by chromatography on silica, eluting with a mixture of ethyl acetate and cyclohexane with a gradient of 50-100% to give methyl 7-(2-bromo-4-fluorobenzenesulfonylamino)-10H-9-oxa-1,2-diaza-phenanthrene-8-carboxylate (0.408 g) as an off-white solid.
