Example 1E Synthesis of 4-(trifluoromethoxy)phenylboronic acid: 1-bromo-4-(trifluoromethoxy)benzene (1.69 kg) and triisopropyl borate (1.46 kg) were dissolved in THF (6.75 L) at -70 °C. A hexane solution (3.27 L) of 2.25 M butyllithium was slowly added to this solution over a period of 2.3 hours, followed by stirring for 10 minutes. Next, the reaction was quenched with 6 M HCl (1.52 L) and stirred at room temperature for 18 hours. The reaction mixture was poured into a mixture of heptane (8.43 L) and 20% (w/w) aqueous sodium chloride solution (8.44 kg) and stirred for 10 min to separate the aqueous and organic phases. The organic phase was concentrated to give a white paste. The paste was dried in vacuum (100 mmHg) at ambient temperature while nitrogen was passed for 2 days. Subsequently, it was further dried at 40-50 °C for 18 h to give 1.306 kg (90.4% yield) of the target product 4-(trifluoromethoxy)phenylboronic acid as a solid. The product was characterized by 1H NMR (CDCl3, 300 MHz): δ 7.24-7.19 (m, 2H), 8.14-8.10 (m, 2H) and additional absorption peaks were observed at δ 7.19-7.15 (m, 2H) and 8.04-8.00 (m, 2H), which corresponded to the cyclic boronic acid trimer.
