General procedure for the synthesis of 3-ethynylpiperidine hydrochloride from 3-ethynylpiperidine-1-carboxylic acid tert-butyl ester: Preparation of Intermediate 35 (Method V); Synthesis of 3-ethynylpiperidine hydrochloride: to Intermediate 33 (1.50 g, 7.18 mmol) was added a dioxane solution (50 mL) of 4 M HCl. The reaction mixture was stirred at room temperature for 16 hours. After completion of the reaction, the mixture was concentrated in vacuum. The residue was ground with ether (Et2O) to give 3-alkynylpiperidine hydrochloride (0.91 g, 86% yield).1H NMR (DMSO-d6) δ: 9.02 (2H, br.s), 3.38-3.24 (1H, m), 3.21-3.08 (2H, m), 2.94-2.76 (3H, m), 2.00-1.87 (1H, m), 1.83-1.73 (1H, m), 1.73-1.60 (1H, m), 1.60-1.48 (1H, m).
