Synthesis
A tetrahydrofuran solution (100 mL) of tert-butyl piperazine-1-carboxylate (9.31 g, 50 mmol), [(1-ethoxycyclopropyl)oxy]trimethylsilane (20.11 mL, 100.00 mmol), and acetic acid (14.31 mL, 250.00 mmol) was treated with sodium cyano-borohydride (4.71 g, 75.00 mmol) to treat methanol (10 mL). The resulting solution was stirred at 60 C for 18 hours. The reaction mixture was cooled, filtered and evaporated to dryness. 1NHCl (40 ml) and water (60 ml) were added and the solution was extracted with ethyl acetate (3 x 50 ml). The aqueous layer was alkalized to pH 10 with solid potassium carbonate and extracted with ethyl acetate (4 x 50 ml). The organic extract was washed with saturated sodium chloride solution (50 ml), dried over MgSO4, filtered and evaporated to dryness to give tert-butyl 4-cyclopropylpiperazine-1-carboxylate (7.73 g, 68.3%) as a white waxy solid.1-Cyclopropylpiperazine dihydrochloride: a dioxane solution of 4.0 MHCl (42.7 mL, 170.78 mmol) was added to the stirred 4 -tert-butyl cyclopropylpiperazine-1-carboxylate (7.73 g, 34.16 mmol) to a stirred mixture of methanol (50.0 mL) and ethyl acetate (200 mL). The resulting suspension was stirred at room temperature under nitrogen for 24 hours. The white solid was filtered to give 1-cyclopropylpiperazine dihydrochloride (6.30 g, 93%).
