Step 3: Synthesis of 3-tert-butyl 3-methyl(S)-piperazine dicarboxylate (AA3); 10% Pd-C (0.2 eq.) was added to a stirred methanolic solution (0.1 M) of AA 2 at room temperature. The reaction mixture was placed under hydrogen atmosphere and stirred at room temperature for 3 hours. After completion of the reaction, the mixture was filtered and the filter cake was washed with methanol. The filtrate was concentrated under reduced pressure to afford the target product methyl (S)-1-N-Boc-3-piperazinecarboxylate in 89% yield. The product was confirmed by 1H NMR (400 MHz, CDCl3,300K): δ 4.05 (1H, m), 3.76 (3H, s), 3.74-3.68 (1H, m), 3.44 (1H, dd, J = 8.6,3.5 Hz), 3.30-3.12 (1H, m), 3.10-3.00 (2H, m), 2.75 ( 1H, m), 2.17-1.74 (1H, m), 1.47 (9H, s). Mass spectrometry analysis (ES +) showed that the theoretical molecular weight of C11H20N2O4 was 244 and the measured value was 267 (M + Na)+.
