L-Proline 86 (2.0 g, 17.4 mmol) was dissolved in methanol (20 mL) and to this solution was added 40% aqueous formaldehyde solution (1.4 mL, 19.1 mmol). This was followed by the addition of 10% palladiumon-charcoal catalyst (500 mg) and the resulting slurry was stirred in a hydrogen atmosphere overnight. The slurry was then filtered through a Celite pad to remove the catalyst. The pad was washed with methanol and the combined filtrates were concentrated under reduced pressure. The residue was taken up in ethanol-benzene (1:1, 100 mL) and concentrated a second time to provide a solid, which was recrystallized from methanol-diethyl ether. In this way N-Methyl-L-proline was isolated as fine needles (2.2 g, 98%). Mp 142-145 °C. [α]23 D -78.0° (c 2.0, MeOH). 1H NMR (300 MHz, D2O) δ 3.71-3.65 and 3.55-3.51 (2m, 1H), 3.00-2.91 (m, 1H), 2.74 (s, 3H), 2.34-2.28 (m, 1H), 1.99-1.78 (m, 3H). 13C NMR (75 MHz, CDCl3) δ 173.06, 70.18, 55.83, 40.26, 28.34, 22.37. IR (KBr disk) ν 3000-2800 (CH, saturated), 2675 and 2605 (ammonium ion), 1669 (CO2H), 1612 (CO2 -), 1468, 1401, 1354, 1327, 1234, 1183, 1112, 1056, 1025, 808, 775 cm-1. HRMS calcd for C6H11NO2 (M+) 129.0790, found 129.0784.
