(2R)-Pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester (2.15 g, 10 mmol) reacted with morpholine (1.3 mL, 15 mmol) in CH2Cl2 (30 mL) in the presence EDC (2.7 g, 15 mmol), HOBT (1.9 g, 15 mmol) and Et3N (2.1 mL, 15 mmol) at r.t. for 14 h. The mixture was evaporated to dryness and purified by column chromatography. After washing the resulting solid with aqueous NaHCO3 followed by H2O to remove HOBT contamination, pure compound (2R)-2-(morpholine-4-carbonyl)-pyrrolidine-1-carboxylic acid tert-butyl ester 11a (1.79 g, 63%) was obtained.
