General procedure for the synthesis of 1-Boc-3,5-dimethylpiperazine from di-tert-butyl dicarbonate and 2,6-dimethylpiperazine: 2,6-dimethylpiperazine (200.0 mg, 1.75 mmol) and triethylamine (TEA, 0.6 mL, 4.37 mmol) were dissolved in dichloromethane (DCM, 6.0 mL), and di-tert-butyl dicarbonate (DTBD, 1.5 mmol, 2.6 mL) was added slowly at 0 °C. butyl dicarbonate ((Boc)2O, 458.7 mg, 2.10 mmol) was added slowly at 0 °C. The reaction mixture was stirred at room temperature for 12 hours and then concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent ratio: DCM:MeOH = 95:5). The fraction containing the target product was collected and evaporated to give tert-butyl 3,5-dimethylpiperazine-1-carboxylate (210.0 mg, 56% yield) as a yellow liquid.1H-NMR (300 MHz, CDCl3) δ: 3.95 (m, 2H), 2.79 (m, 2H), 2.33 (m, 2H), 1.46 (s, 9H), 1.07 (d. 6H, J = 6.3 Hz).
