To a solution of 6-cyano-4-ethoxycarbonyl-2,3-dihydro-1,4-benzoxazine-2-carboxylic acid (552 mg, 2.0 mmol) and (5-amino-4-bromo-2-cyclopentyl-phenyl)methyl carbonate (691 mg, 2.20 mmol) in 2-methyltetrahydrofuran (7 mL) at room temperature was added pyridine (404 μL, 5.0 mmol) followed by the addition of T3P (3181 mg, 2.98 mL of 50% w/w solution, 5.0 mmol). The reaction was stirred at room temperature for 1 h. The reaction mixture was diluted with ethyl acetate then quenched with a saturated aqueous solution of NaHCO3 (4 mL) and stirred for 15 min. The layers were separated, and the aqueous layer was extracted once more with ethyl acetate. The combined organic extracts were filtered to give a white solid. The remaining filtrate was dried over Na2SO4, filtered and concentrated in vacuo to obtain a creamy solid. The combined solids were triturated with hexane (5×5 mL) and washed with ethyl acetate (1 mL) and dichloromethane (1 mL) to provide ethyl 2-(2-bromo-4-cyclopentyl-5-(methoxycarbonyloxy)phenylcarbamoyl)-6-cyano-2H-benzo[b][1,4]oxazine-4(3H)-carboxylate as a white solid (403 mg, 99% yield). LC/MS m/z 573.1 [M+H]+.
