Example 4a Preparation of 2-bromo-4-hydrazinobenzonitrile: Anhydrous hydrazine (10 mL) was slowly added to a solution of 2-bromo-4-fluorobenzonitrile (5.00 g, 25.00 mmol) in tetrahydrofuran (THF, 10 mL) through an addition funnel under dry conditions. After the addition was completed, the reaction mixture was stirred at room temperature for 24 hours. Upon completion of the reaction, water (20 mL) was added to the mixture to quench the reaction. The resulting white precipitate was collected by diafiltration and washed well with deionized water. Subsequently, the product was dried in a vacuum oven at 40 °C to afford 2-bromo-4-hydrazinylbenzonitrile (4.92 g, 93% yield) as a white solid. The structure of the product was confirmed by 1H NMR (300 MHz, CDCl3): δ 8.05 (br s, 1H), 7.47 (d, J = 8.7 Hz, 1H), 7.06 (d, J = 2.0 Hz, 1H), 6.72 (dd, J = 8.7, 2.0 Hz, 1H), 4.37 (br s, 2H); ESI MS m/z 212 [M + H]+.
