[NH2:1][CH2:2][CH2:3][CH:4]1[CH2:9][CH2:8][N:7]([C:10]([O:12][C:13]([CH3:16])([CH3:15])[CH3:14])=[O:11])[CH2:6][CH2:5]1.C=O.[C:19](O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+]>C(Cl)Cl.C(O)(=O)C>[CH3:19][NH:1][CH2:2][CH2:3][CH:4]1[CH2:5][CH2:6][N:7]([C:10]([O:12][C:13]([CH3:16])([CH3:15])[CH3:14])=[O:11])[CH2:8][CH2:9]1Tert-butyl 4-(2-aminoethyl)piperidine-1-carboxylate (1.0 g, 4.38 mmol) was dissolved in DCM (40 ml) and treated with 36.5% formaldehyde solution (326 μl, 4.38 mmol) followed by acetic acid (1 drop). The reaction mixture was stirred for 20 mins and treated with sodium triacetoxyborohydride (93 mg, 0.438 mmol). The resulting mixture was stirred at ambient temperature for 16 hrs and quenched with 2M NaOH (40 ml). The mixture was extracted with DCM (2×100 ml) and the combined organic extracts were dried (MgSO4) and concentrated under reduced pressure to give tert-butyl 4-(2-(methylamino)ethyl)piperidine-1-carboxylate as an oil;
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