General procedure for the synthesis of 3,5-dibromo-1-methylpyridin-2(1H)-one from 3,5-dibromo-2-hydroxypyridine and iodomethane: 3,5-dibromo-1H-pyridin-2-one (5 g, 19.8 mmol) was dissolved in DMF (170 mL), K2CO3 (6.01 g, 43.5 mmol) was added and the suspension was stirred for 15 min. Subsequently, MeI (1.36 mL, 21.8 mmol) was added dropwise to the reaction system and the reaction was stirred at room temperature for 18 hours. After completion of the reaction, water (200 mL) was added to the mixture and the aqueous layer was extracted with EtOAc (3 x 200 mL). The organic layers were combined, dried with Na2SO4, filtered and concentrated under reduced pressure. The resulting solid was ground with Et2O to give 3,5-dibromo-1-methylpyridin-2(1H)-one (2 g). The filtrate was evaporated under reduced pressure and the residue was ground with Et2O to give a second product (2.0 g). The filtrate was further concentrated and purified by fast chromatography on silica gel, using a solvent mixture of EtOAc and hexane as eluent, to give finally 3,5-dibromo-1-methylpyridin-2(1H)-one (4.5 g total, 85% yield). The product was characterized by 1H NMR (500 MHz, CDCl3): δ 7.78 (d, J=2.5 Hz, 1H), 7.42 (d, J=2.5 Hz, 1H), 3.59 (s, 3H). Mass spectra (ESI) showed [M+H]+ peaks of 266.01, 267.99, 269.99.
