General procedure: synthesis of tert-butyl 4-(2-hydroxyethyl)piperazine-1-carboxylate (57): 1-(2-hydroxyethyl)piperazine (3.0 g, 23.0 mmol) was dissolved in dry tetrahydrofuran (THF) under nitrogen protection. Subsequently, di-tert-butyl dicarbonate (5.5 g, 25.3 mmol) was slowly added to this solution. The reaction mixture was stirred at room temperature for 2 hours. After completion of the reaction, the solvent was evaporated to half of the initial volume by rotary evaporator. The concentrated mixture was poured into deionized water and extracted with dichloromethane (CH2Cl2). The organic phases were combined, washed with saturated saline and dried over anhydrous sodium sulfate (Na2SO4). After filtration, the filtrate was concentrated under reduced pressure to afford the light yellow oily product tert-butyl 4-(2-hydroxyethyl)piperazine-1-carboxylate (5.3 g, quantitative yield). The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3): δ 1.46 (s, 9H), 2.44-2.46 (m, 4H), 2.54-2.57 (m, 2H), 2.66 (m, J = 5.3 Hz, 1H), 3.42-3.45 (m, 4H), 3.62 (q, J = 5.3 Hz, 2H).
