General procedure for the synthesis of 2-methyl-3-chloro-5-bromopyridine from diethyl 2-(5-bromo-3-chloropyridin-2-yl)malonate: firstly, impure diethyl 2-(5-bromo-3-chloropyridin-2-yl)malonate (Intermediate 42, 0.41 g, 1.2 mmol) was dissolved in a concentrated aqueous hydrochloric acid solution (3 mL), and heated and refluxed for 3 hours. Upon completion of the reaction, volatiles were removed by vacuum distillation and the residue was co-evaporated with acetonitrile. Subsequently, the resulting monodeoxycarboxylic acid solid was dissolved in dioxane (4.5 mL) and heated to reflux overnight. The volatiles were again removed by vacuum distillation. Finally, the residue was purified by fast chromatography (using 4 g SiO2, heptane/EtOAc gradient elution) to afford the target product 2-methyl-3-chloro-5-bromopyridine (0.12 g, 51% yield). The product was characterized by 1H NMR (500 MHz, CDCl3): δ 2.60 (s, 3H), 7.82 (d, 1H), 8.46 (d, 1H); the mass spectrum (CI) showed m/z 206 [M + H]+.
