(S)-4-N-Boc-piperazine-2-carboxylic acid → [(2S)-4-methylpiperazin-2-yl]methanol

To a stirred suspension of (S)-piperazine-1,3-dicarboxylic acid 1-tert-butyl ester (5.00 g, 21.7 mmol) in THF (40 mL) was slowly added 1.0 M borane-THF complex solution (32.6 mL, 32.6 mmol). The reaction was heated to 90° C. and stirred under reflux for 2 hours. The reaction mixture was removed from the heat before a further 1.5 equivalents of 1.0 M borane·THF complex solution (32.6 mL, 32.6 mmol) was added. The reaction was re-heated to 90° C. and stirred under reflux for a further 2 hours. The reaction was cooled to 0° C. and quenched by the slow addition of MeOH. The reaction mixture was then concentrated in vacuo. The white solid obtained was dissolved in THF (30 mL), cooled to 0° C. and slowly added a 2.0M solution of LiAlH4 in THF (27 mL, 54.0 mmol). The reaction was heated to 90° C. and stirred under reflux for 2 h. A further portion of 2.0M solution of LiAlH4 in THF (27 mL, 54.0 mmol) was added and the reaction stirred under reflux for 4 h and then at room temperature overnight. The reaction mixture was cooled to 0° C. and quenched by the slow addition of 1.0M aq NaOH solution until the exothermic reaction subsided. The resulting gel was diluted with THF and the solids filtered off. The filtrate was then concentrated in vacuo to afford (S)-(4-methyl-piperazin-2-yl)-methanol (2.84 g, 101% crude yield) as a colourless oil.