Under ice-cooling, 60% sodium hydride (0.21 g) was added to an N,N-dimethylformamide (15 mL) solution of methyl 4-(2-(tert-butoxycarbonylamino)phenyl)-2-nitrobenzoate (1.3 g), followed by stirring at room temperature for 10 minutes. Then, methyl iodide (0.32 mL) was added thereto under ice-cooling, followed by stirring at room temperature for 1 hour. Water, a 10% aqueous solution of citric acid, and diethyl ether were added to the reaction mixture. The organic layer was separated, washed with a saturated aqueous solution of sodium chloride, and dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography [eluent: 95-85% hexane/ethyl acetate] to obtain 1.1 g of methyl 4-(2-((tert-butoxycarbonyl)(methyl)amino)phenyl)-2-nitrobenzoate as a light yellow solid.
