To a solution of 4-(1-piperazinyl)phenol (2.0 g, 11.22 mmol) in water (56 mL) was added sodium hydroxide (673 mg, 16.83 mmol) followed by di-tert-butyl dicarbonate (2.7 g, 12.34 mmol). The reaction mixture was stirred at room temperature overnight. On the next day, the reaction mixture was filtered and tert-butyl 4-(4-hydroxyphenyl)piperazine-1-carboxylate was collected as a brown solid (3.1 g, 99% yield), which was washed with water (50 mL) and used for the next reaction without further purification.1H NMR (300 MHz, DMSO-d6): δ 6.79 (AA'BB', 2H, JAB = 9.1 Hz. JAA' = 2.4 Hz), 6.66 (AA'BB', 2H, JAB = 9.1 Hz, JBB' = 2.4 Hz), 3.43 (dd, 4H, J = 5.3,4.9 Hz), 2.88 (dd, 4H, J = 5.2,5.1 Hz), 1.41 (s, 9H); 13C NMR (75.5 MHz, DMSO-d6 ): δ153.8,151.4,144.0,118.5,115.4,78.8,50.3,28.0.
