Hydrochloric Acid → Methyl 1-(2-chloroethyl)piperidine-4-carboxylate

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To a solution of 1-tert-butyl 4-methyl piperidine-1,4-dicarboxylate (5.4 g, 22.19 mmol) in ether was added hydrogen chloride (27.7 mL, 111 mmol) in dioxane. The resulted clear solution was stirred for 4 hours. Bubbles and white precipitates were observed. Then the solvent was removed and dried in vacuo. The residue was suspended in acetonitrile (50 mL), and 2-bromoethanol (1.567 mL, 22.19 mmol) was added followed by powdered K2CO3 (14.72 g, 107 mmol). After the reaction mixture was refluxed for 18 hours, it was filtered and concentrated. The residue was redissolved in water (50.0 mL) and extracted with ethyl acetate (50.0 mL). The organic layer was dried over sodium sulfate. After filtration the solvent was removed in vacuo. The residue was dissolved in DCE (50.0 mL) before sulfurous dichloride (2.428 mL, 33.3 mmol) was added. The reaction mixture was reflux for 3 hours, then all volatile was removed in vacuo, the resulting solid was suspended in ether, then filtered and washed with ether (50.0 mL), resuspended in ethyl acetate and neutralized with sodium bicarbonate. The organic layer was collected and dried with sodium sulfate to afford methyl 1-(2-chloroethyl)piperidine-4-carboxylate (1 g, 4.86 mmol, 21.91% yield) as a brown oil. 1H NMR (400 MHz, CHLOROFORM-d) δ 3.70 (s, 3H), 3.61 (t, J=7.0 Hz, 2H), 2.97-2.86 (m, 2H), 2.75 (t, J=7.2 Hz, 2H), 2.40-2.27 (m, 1H), 2.19 (m, 2H), 2.01-1.88 (m, 2H), 1.87-1.72 (m, 2H).

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