General procedure for the synthesis of 1,4-bis(tert-butoxycarbonyl)piperazine from piperazine and di-tert-butyl dicarbonate: In a 10 mL round bottom flask, EtOH (5 mL), di-tert-butyl dicarbonate (1-2 mmol), nano-Fe3O4 catalyst (3 mol%, 0.007 g) and piperazine (1 mmol) were added. The reaction mixture was stirred at room temperature until complete (refer to Table 3 for reaction times). After completion of the reaction, the nano-Fe3O4 catalyst was separated using external magnet adsorption. The separated solution was dried and the solvent was concentrated, and the resulting crude product was recrystallized with hexane or ethyl acetate (5 mL) to give pure 1,4-bis(tert-butoxycarbonyl)piperazine. The recovered Fe3O4 nanocatalyst was washed with EtOH and dried, and could be reused. The catalyst was recycled six times without significant changes in the reaction yield and time.
[1] Tetrahedron Letters, 2009, vol. 50, # 46, p. 6244 - 6246
[2] Synthetic Communications, 2012, vol. 42, # 1, p. 25 - 32
[3] Tetrahedron Letters, 2007, vol. 48, # 47, p. 8318 - 8322
[4] Comptes Rendus Chimie, 2013, vol. 16, # 11, p. 962 - 966
[5] Chinese Journal of Catalysis, 2013, vol. 34, # 9, p. 1730 - 1733
