General procedure for the synthesis of 1-bromo-4-(2-bromoethyl)benzene with n-butylmagnesium chloride as a raw material for the synthesis of 1-bromo-4-hexylbenzene: coupling reaction of alkyl halides with t-BuMgCl. Step 1 (P1): alkyl halides (1.0 mmol), decane (63 mg, as an internal standard) and LiI (5.3 mg, 0.04 mmol) were added to a reaction tube equipped with a rubber septum and a magnetic stirrer under a dry nitrogen atmosphere. THF (0.8 mL) was then added and the solution was cooled to -78 °C using a dry ice/EtOH bath. Slowly t-BuMgCl(2a) (1.5 mL, 0.81 M of THF solution, 1.2 mmol) was added, followed by isoprene (136.2 mg, 2.0 mmol). To this mixture was added CoCl2 [2.6 mg, 0.02 mmol, as a powder or as a THF solution (0.5 mL, 0.04 M)]. (Note 1: CoCl2 should be added immediately after isoprene addition or the catalytic efficiency will be significantly reduced.) Remove the cold bath, warm the mixture slowly to room temperature (about 10 min), and then heat the reaction vessel in a 50°C oil bath for 5 hr. (Note 2: If the reaction mixture is heated at 30 °C at this stage, unidentified side reactions can occur, resulting in lower yields of coupling products.) Upon completion of the reaction, the mixture is cooled to 0 °C in an ice bath and the reaction is quenched with 1 M aqueous HCl (5 mL). The product was extracted with Et2O (3 x 20 mL). The organic layers were combined, dried with Na2SO4, concentrated and analyzed by gas chromatography to determine the GC yield. The residue was purified by silica gel column chromatography or GPC. Under standard conditions, 1.0 mmol of 1-bromo-4-(2-bromoethyl)benzene was reacted with n-BuMgCl(2j) (1.0 M in THF, 1.2 mmol) in 94% yield (determined by GC using decane as an internal standard).
