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General procedure for the synthesis of ethyl 3-methylpiperidine-3-carboxylate hydrochloride from ethyl 1-Boc-3-methylpiperidine-3-carboxylate: 24.2 g (84.8 mmol) of 1-tert-butyl 3-ethyl 3-methylpiperidine-1,3-dicarboxylate was added to 50 mL of ethyl acetate solution of 2.5 M hydrochloric acid. The reaction mixture was stirred at 20°C for 3 hours, then 100 mL of diethyl ether was added. The precipitated crystals were filtered and washed with diethyl ether to give 16.28 g (97% yield) of ethyl 3-methylpiperidine-3-carboxylate hydrochloride.

[1] Patent: WO2018/167630, 2018, A1. Location in patent: Page/Page column 29
[2] Patent: WO2018/167629, 2018, A1. Location in patent: Page/Page column 25