General procedure for the synthesis of (R)-1-(tert-butoxycarbonyl)-2-methylpyrrolidine-2-carboxylic acid from the compound (CAS: 912445-03-5):
Step 74D: Synthesis of (R)-2-methylpyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester
A 5% palladium-carbon catalyst (2.56 g) was added to the pressure reactor and the reactor was purged with nitrogen. The Example 74C product (α60wt% isopropyl acetate solution, 83.1 g) and denatured ethanol (335 g) were then added. The reactor was pressurized with hydrogen (40 psig) and the hydrogenolysis reaction was carried out while controlling the reaction temperature to not exceed 40°C. Upon completion of the reaction, the catalyst was removed by filtration to give a product with a measured yield of 97% and an enantiomeric excess (ee) of 93.9%.
Post-treatment step: the solvent was removed by distillation under vacuum and solvent replacement was carried out with isopropyl acetate (240 g). This was followed by the addition of heptane (200 g) for further replacement, then additional heptane (500 g) was added and the mixture was heated to reflux until all solids were completely dissolved. After cooling the solution to 20°C, the solid product was collected by filtration, washed with heptane (80 g) and dried to give 54.8 g of Example 74D product in 88% yield.
Product characterization: 1H NMR (400 MHz, CDCl3, rotary isomer mixture) δ ppm 1.42 (s) and 1.47 (s), (9H); 1.52 (s) and 1.61 (s) (2H); 1.73-2.05 (m, 3H); 2.19-2.38 (m) and 2.46-2.67 (m) (1H); 3.26- 3.71 (m, 2H).
