N-bromobutanimide → 8-Bromo-5-hydroxy-2-oxo-1,3-diphenyl-1,2-dihydro-[1,7]naphthyridine-6-carboxylic acid methyl ester

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A mixture of 5-hydroxy-2-oxo-1,3-diphenyl-1,2-dihydro-[1,7]naphthyridine-6-carboxylic acid methyl ester (138 mg, 0.37 mmol) and N-bromosuccinimide (73 mg, 0.41 mmol) in CH2Cl2 (1.5 mL) was refluxed for 3.5 h. Solvent was evaporated in vacuo, and the residue was purified twice by silica gel chromatography (0-100% EtOAc/hexanes+1% AcOH, then 30-100% CH2Cl2/hexanes) to give 114 mg of the title compound as a pale yellow solid. MS: (+) m/z 451.25, 453.01 (M+1, 79/81Br).

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