General procedure for the synthesis of tert-butyl (R)-2-thiocarboxamido pyrrolidine-1-carboxylate from N-tert-butoxycarbonyl-L-prolinamide: (S)-1-(tert-butoxycarbonyl)prolinamide (9.0 g, 42.0 mmol) and Lawesson's reagent (8.5 g, 21.0 mmol) were dissolved in anhydrous THF (55 mL) and the reaction was stirred for 3.5 hours at room temperature under nitrogen protection. The reaction was stirred at room temperature for 3.5 h under nitrogen protection. After completion of the reaction, the solvent was removed by distillation under reduced pressure. Saturated aqueous NaHCO3 (100 mL) was added to the residue and stirring was continued for 1 hour. The aqueous phase suspension was extracted with EtOAc/CH2Cl2 (1:1, 400 mL), the organic phase was washed with saturated aqueous NaHCO3 solution (2 x 100 mL), and the combined aqueous phases were then extracted with EtOAc/CH2Cl2 (200 mL). All organic extracts were combined, dried with Na2SO4 and concentrated under reduced pressure to give tert-butyl (S)-2-thiocarbonylpyrrolidine-1-carboxylate as a white solid (8.74 g, 90% yield) with a melting point (EtOAc) of 190-192 °C. [α]D -103.4 (c 1.00, CHCl3). IR (KBr) 3380, 3202, 2981, 2881, 1671, 1411, 1166 cm-1. 1H NMR (400 MHz, CDCl3) δ= 1.41-1.50 (m, 9H), 1.65-2.75 (m, 4H), 3.22- 3.74 (m, 2H), 4.67 (dd, J = 8.0 and 3.6 Hz, 1H) ppm. HRMS (ESI) m/z calculated value C10H19N2O2S (M + H) 231.1162, measured value 231.1161.
