[CH2:1]([O:3][C:4]([C@H:6]1[C@H:10]([C:11](O)=[O:12])[CH2:9][N:8]([C:14]([O:16][C:17]([CH3:20])([CH3:19])[CH3:18])=[O:15])[CH2:7]1)=[O:5])[CH3:2].CSC.B.CO>C1COCC1>[CH2:1]([O:3][C:4]([C@H:6]1[C@H:10]([CH2:11][OH:12])[CH2:9][N:8]([C:14]([O:16][C:17]([CH3:18])([CH3:20])[CH3:19])=[O:15])[CH2:7]1)=[O:5])[CH3:2]To a solution of (3S*,4S*)-pyrrolidine-1,3,4-tricarboxylic acid 1-tert-butyl ester 3-ethyl ester (10 g, 34.8 mmol) in THF (180 mL), a solution of borane dimethylsulfide complex (2N in THF, 24.4 mL, 48.7 mmol) is added slowly at −10° C. The mixture is stirred at −10° C. for 20 min, then allowed to reach RT and further stirred for 4 h. MeOH is carefully added (exothermic!), and the mixture is concentrated under reduced pressure. MeOH is again added, and the mixture is concentrated. This operation is repeated 3 times, then the mixture is finally taken up into a saturated aqueous solution of NaHCO3 and extracted 3 times with CH2Cl2. The combined organic extracts are dried over Na2SO4, filtered and concentrated. The crude material is purified by flash chromatography on silica gel (eluent: CH2Cl2/MeOH from 100:0 to 95:5) to give the title compound as product. TLC, Rf (AcOEt)=0.52. MS (LC-MS): 174.1 [M+H-Boc]+.
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