General procedure for the synthesis of 1-Boc-4-piperidinecarboxylic acid from methyl 1-Boc-4-piperidinecarboxylate: 4-tert-butyl-4-methylpiperidine-1,4-dicarboxylate (4.84 g, 20 mmol) and LiOH (2.52 g, 60 mmol) were reacted with 4-tert-butyl-4-methylpiperidine-1,4-dicarboxylate (4.84 g, 20 mmol) and LiOH (2.52 g, 60 mmol) in a mixture of THF (90 mL), MeOH (90 mL) and H2O (30 mL) in a solvent, and the reaction was stirred at room temperature overnight. After completion of the reaction, the solvent was removed by distillation under reduced pressure. The residue was adjusted to pH 2 with aqueous 2N HCl. Subsequently, the reaction mixture was extracted with EtOAc (3 × 20 mL). The organic phases were combined, dried over anhydrous Na2SO4 and concentrated under reduced pressure to give 1-(tert-butoxycarbonyl)piperidine-4-carboxylic acid (4.6 g, 100.0% yield).
