C(=O)([O-])[O-].[K+].[K+].[C:7]([OH:10])(=[S:9])[CH3:8].CS(O[CH:16]1[CH2:20][CH2:19][N:18]([C:21]([O:23][C:24]([CH3:27])([CH3:26])[CH3:25])=[O:22])[CH2:17]1)(=O)=O>CO.CN(C=O)C.O>[C:7]([S:9][CH:20]1[CH2:16][CH2:17][N:18]([C:21]([O:23][C:24]([CH3:27])([CH3:26])[CH3:25])=[O:22])[CH2:19]1)(=[O:10])[CH3:8]
Potassium carbonate (4.42 g, 31.96 mmol) was suspended in dry MeOH (20 mL) and thioacetic acid (2.28 g, 29.96 mmol) was added. The mixture was stirred vigorously for 10 mins, concentrated and diluted in dry DMF (30 mL). tert-Butyl 3-[(methylsulfonyl)oxy]pyrrolidine-1-carboxylate (2.65 g, 9.99 mmol) dissolved in dry DMF (20 mL) was added and the reaction mixture was heated to 60° C. for 3.5 h. The reaction mixture was diluted with water (350 mL) and extracted with EtOAc (2×150 mL) The organic phases were dried with MgSO4, filtered and evaporated. The crude product was purified using Biotage Horizon HPFC system (25+M column, isocratic run heptane/EtOAc (60:40)) affording the title compound (0.592 g, 24.2%) (the product is a mixture of cis and trans isomers). 1H NMR (500 MHz, CDCl3): δ 1.41 (d, 18H), 1.66 (d, 1H), 1.74-1.86 (m, 2H), 2.20-2.26 (m, 2H), 2.29 (s, 3H), 3.10-3.26 (m, 2H), 3.30-3.43 (m, 4H), 3.46-3.54 (m, 1H), 3.66-3.74 (m, 2H); 13C NMR (125 MHz, CDCl3): δ 28.68, 30.82, 31.25, 32.34, 36.16, 41.09, 44.88, 51.60, 55.37, 79.67, 154.43; Mass Spectrum: M+H+ 241.
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