(ii) Preparation of 53c: 4-(4-methylpiperazin-1-yl)phenylboronic acid
To a solution of 53b (390 mg, 1.52 mmol) and THF (10 mL), n-butyllithium (0.79 mL, 2.5 M hexane solution) was slowly added at -78 °C and stirred for 10 min. Subsequently, triisopropyl borate (1.75 mL, 7.64 mmol) was added at the same temperature. The reaction mixture was slowly warmed to room temperature and then the reaction was quenched with phosphoric acid. The reaction mixture was neutralized with saturated NaHCO3 solution and subsequently extracted with EtOAc (3 x 10 mL). The organic phases were combined, dried with anhydrous Na2SO4, filtered and concentrated under reduced pressure. The residue was purified by column chromatography (silica gel, 0-10% MeOH in CH2Cl2 solution) to afford the target product 4-(4-methyl-1-piperazinyl)phenylboronic acid (180 mg, 58%).
1H NMR (300 MHz, CD3OD) δ 2.32 (s, 3H), 2.55 (m, 4H), 3.03 (s, 1H), 3.21 (m, 3H), 6.69-7.59 (m, 4H).
