To a stirred mixture of (S)-4-(tert-butoxycarbonyl)piperazine-2-carboxylic acid (1.0 g, 4.34 mmol) and Na2CO3 (0.90 g, 10.80 mmol) in water (10 mL) was added solution of FMOC-Cl (1.23 g, 4.77 mmol) in 1,4-dioxane (10 mL) dropwise at 0° C. The reaction mixture was stirred at room temperature for 16 h then diluted with water (50 mL) and washed with MTBE (25 mL). The aqueous layer was acidified with 1N aqueous HCl (10 mL) to pH 2 and extracted with EtOAc (3×50 mL). The combined organic extracts were washed with brine solution (50 mL), dried over anhydrous Na2SO4, filtered and concentrated to afford the title compound (0.87 g) as an off-white solid. The crude product was used in the next step without purification.
