Cl.[NH:2]1[CH2:6][CH2:5][CH2:4][C@H:3]1[C:7]([O:9][CH2:10][C:11]1[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=1)=[O:8].C([O-])([O-])=O.[K+].[K+].Br[CH2:24][C:25]([O:27][C:28]([CH3:31])([CH3:30])[CH3:29])=[O:26]>CN(C=O)C>[C:28]([O:27][C:25](=[O:26])[CH2:24][N:2]1[CH2:6][CH2:5][CH2:4][C@H:3]1[C:7]([O:9][CH2:10][C:11]1[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=1)=[O:8])([CH3:31])([CH3:30])[CH3:29]To a suspension of (S)-benzyl pyrrolidine-2-carboxylate hydrochloride (700 mg, 2.90 mmol) and K2CO3 (1201 mg, 8.69 mmol) in DMF (7 ml), t-butyl bromoacetate (0.535 ml, 3.62 mmol) is added. After stirring for 71 hours, aqueous K2CO3 (1.5 g of K2CO3/40 ml of H2O) is added to the reaction mixture. The products are extracted with EtOAc. The organic layer is washed twice with water and once with brine, dried over K2CO3, filtered, and concentrated to give (S)-benzyl 1-(2-tert-butoxy-2-oxoethyl)pyrrolidine-2-carboxylate (458 mg); HPLC retention time=1.38 minutes (condition D); MS (m+1)=320.2; 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.44 (s, 9 H) 1.81-2.03 (m, 3 H) 2.13-2.14 (m, 1 H) 2.82-2.88 (m, 1 H) 3.13-3.17 (m, 1 H) 3.46 (A of AB, J=17.3 Hz, 1 H) 3.49 (B of AB, J=17.3 Hz, 1 H) 3.73 (dd, J=8.8 and 4.8 Hz, 1 H) 5.15 (A of AB, J=12.4 Hz, 1 H) 5.17 (B of AB, J=12.4 Hz, 1 H) 7.29-7.38 (m, 5 H).
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