N-Boc-alpha-methyl-L-proline

24424-99-5

42856-71-3

103336-06-7

(S)-2-methylpyrrolidine-2-carboxylic acid hydrochloride (23; 82.5 g, 498 mmol) was dissolved in a solvent mixture of acetonitrile/water (1:1, 1000 mL) and triethylamine (TEA, 210 mL, 1490 mmol) was added. Subsequently, di-tert-butyl dicarbonate (Boc2O, 120 g, 548 mmol) dissolved in acetonitrile (200 mL) was added. The reaction mixture was stirred at room temperature for 3 hours. The organic solvent was removed by evaporation under reduced pressure and 2M aqueous sodium hydroxide (300 mL) was added to the residue. The aqueous phase was extracted with ether (Et2O, 400 mL), cooled to 10 °C and the pH was adjusted to 5-6 by slow addition of 25% aqueous hydrochloric acid. 1M aqueous hydrochloric acid was then carefully added to pH=2 and the product precipitated. The precipitate was collected by filtration, washed with water (300 mL), and dried under high vacuum to give (S)-1-(tert-butoxycarbonyl)-2-methylpyrrolidine-2-carboxylic acid (24, 90.7 g) as a light gray solid. lc-MS: tR = 0.63 min; [M + H]+ = 230.24.