Synthesis
(2) 5.0 g (0.0434 mol) of L-proline was dissolved in 92 mL of 97% formic acid and the reaction temperature was maintained at 5°C-10°C. 30 mL of acetic anhydride was added slowly and the reaction mixture was stirred continuously for 2 hours. After completion of the reaction, the reaction was quenched by adding 35 mL of ice water at room temperature. The solvent was removed by evaporation to afford (S)-(-)-N-formylproline ([α]D2: -105°, c = 2.885, methanol), the product was a clarified, viscous, light yellow oil, which could be used for the next reaction without further purification. Under nitrogen protection, 20 mL of tetrahydrofuran solution of (S)-(-)-N-formylproline was slowly added to 125 mL of tetrahydrofuran suspension of 8.23 g (0.217 mol) of lithium aluminium hydride, and the rate of addition was controlled to maintain mild reflux. After addition, the reaction was continued at reflux for 48 hours. At the end of the reaction, it was cooled to room temperature and the reaction was quenched by careful addition of 8.3 mL of water, 8.3 mL of 15% aqueous sodium hydroxide solution and 25 mL of water in that order. The off-white mixture obtained was filtered and the filtrate was dried over magnesium sulfate and concentrated to an oil. Purification by bulb-to-bulb distillation (oven temperature 40°C-55°C, 0.15 Torr) afforded 2.823 g of N-methyl-L-prolinol in 57% yield (as L-proline).
References
[1] Patent: US4321387, 1982, A
[2] Journal of the Chemical Society - Perkin Transactions 1, 1997, # 19, p. 2891 - 2896
[3] Tetrahedron Letters, 1995, vol. 36, # 43, p. 7885 - 7888
[4] Journal of the American Chemical Society, 1991, vol. 113, # 24, p. 9286 - 9292
[5] Tetrahedron Letters, 1983, vol. 24, # 33, p. 3513 - 3516
