General procedure for the synthesis of 2-bromo-1,3-dimethyl-4-nitrobenzene from 2,6-dimethylbromobenzene:
Step 1: At -10°C, 2-bromo-1,3-dimethylbenzene (5.0 g, 27.03 mmol) was dissolved in 98% sulfuric acid (40 mL), and a mixed solution consisting of 68% nitric acid (2.74 g, 27.03 mmol) and 98% sulfuric acid (10 mL) was slowly added dropwise. After the reaction was completed, the mixture was continued to be stirred at -10°C for 1 hour. Subsequently, the reaction mixture was quenched by pouring it into ice (200 g), the precipitated solid was collected by filtration, washed with water and dried under vacuum. The crude product was purified by silica gel column chromatography using petroleum ether/ethyl acetate (100:1) as eluent to afford 2.3 g (37% yield) of 2-bromo-1,3-dimethyl-4-nitrobenzene as a yellow solid. The structure of the product was confirmed by 1H NMR (500 MHz, DMSO-d6): δ 7.79 (d, J=8.5 Hz, 1H), 7.43 (d, J=8.5 Hz, 1H), 2.47 (s, 3H), 2.44 (s, 3H).
