General procedure for the synthesis of 3,5-dibromobenzonitrile from 1,3,5-tribromobenzene: iPrMgCl (2M in THF, 4.1 mL) and THF (5 mL) were added to a flask containing dry LiCl (0.35 g, 8.24 mmol) at 15 °C. After stirring for 15 min, a solution of 3-bromobenzonitrile (1.46 g, 8.03 mmol) in THF (1 mL) was slowly added to the reaction mixture and stirring was continued for 15 min. Subsequently, DMF (1.3 mL, 12 mmol) was slowly added at 0 °C and the mixture was stirred for 2 hours. After completion of the reaction, aqueous NH3 (7 mL, 28-30%) and I2 (4.06 g, 16 mmol) were added to the mixture and stirred for 2 h at room temperature. The reaction mixture was poured into saturated aqueous Na2SO3 solution and extracted with CHCl3 (3 x 30 mL). The organic layers were combined, dried with Na2SO4 and filtered. After removing the solvent under reduced pressure, the residue was purified by silica gel column chromatography (eluent: hexane/ethyl acetate = 9:1, v/v) to afford pure 3,5-dibromobenzonitrile (0.73 g) in 71% yield. Most of the nitrile compounds involved in this study were commercially available and were identified by comparison with authentic samples.
