The general procedure for the synthesis of 1,4-dibromo-2,3-dimethylbenzene from 4-bromo-2,3-dimethylaniline hydrobromide was as follows: first, a solution of free base 3b was prepared. 4-Bromo-2,3-dimethylaniline hydrobromide (8.69 g, 43.5 mmol) was suspended in Et2O (20 mL), Na2CO3 (5 g, 50 mmol) and H2O (5 mL) were added, stirred, and then filtered and the solvent was evaporated to obtain the free base 3b.Next, the free base 3b was dissolved in MeCN (100 mL), and this solution was added to the MeCN (200 mL) solution containing CuBr2 (9.71 g, 43.5 mmol, 1 eq.) and tBuONO (4.93 g, 5.68 mL, 47.8 mmol, 1.1 eq.). The reaction mixture was stirred at room temperature for 16 hours and then at 82 °C for 4 hours. Upon completion of the reaction, the mixture was cooled to room temperature, diluted with AcOEt (200 mL), washed sequentially with brine (2 x 100 mL), dried (MgSO4), and the solvent was evaporated to afford the target product 1,4-dibromo-2,3-dimethylbenzene (9.79 g, 85% yield). The NMR data of the product were in agreement with those reported in the literature ref15.
