General procedure for the synthesis of 2-bromo-3-nitro-5-methylpyridine from 2-hydroxy-3-nitro-5-methylpyridine: at a low temperature of 0-10°C, phosphorus tribromide (POBr3, 222.8 g, 0.78 mol) was added batchwise to an N,N- dimethylformamide (DMF, 500 mL) solution. Subsequently, the reaction mixture was warmed to 80 °C and stirred continuously for 12 h under nitrogen protection. Upon completion of the reaction, the mixture was cooled to room temperature and quenched by slowly pouring into crushed ice (1 Kg). The resulting solid product was collected by filtration and washed well with ice-cold deionized water (2 x 500 mL) to remove impurities. Finally, the resulting solid was placed in a desiccator and dried under high vacuum for 24 h to afford the target compound 2-bromo-5-methyl-3-nitropyridine as a yellow solid (121 g) in 86% yield. Results of mass spectrometry analysis: (M+H)+ theoretical value: 217; measured value: 216.9.
