[C:1]([O:5][C:6]([NH:8][C@@H:9]1[CH2:12][C@H:11]([C:13]([OH:15])=[O:14])[C:10]1([CH3:17])[CH3:16])=[O:7])([CH3:4])([CH3:3])[CH3:2].C([O-])([O-])=O.[Cs+].[Cs+].[CH:24]1[CH:29]=[CH:28][C:27]([CH2:30]Br)=[CH:26][CH:25]=1>CN(C=O)C.CCOC(C)=O>[C:1]([O:5][C:6]([NH:8][C@@H:9]1[CH2:12][C@H:11]([C:13]([O:15][CH2:30][C:27]2[CH:28]=[CH:29][CH:24]=[CH:25][CH:26]=2)=[O:14])[C:10]1([CH3:17])[CH3:16])=[O:7])([CH3:4])([CH3:2])[CH3:3]A stirred solution of (1S,3R)-3-(tert-butoxycarbonylamino)-2,2-dimethylcyclobutanecarboxylic acid (0.5 g, 2.05 mmol) in DMF (about 5 ml), Cs2CO3 (0.804 g, 2.47 mmol) and BnBr (0.3 ml, 2.47 mmol) were added slowly portion wise at about 0° C., then the reaction was stirred at room temperature for about 2 hours. After completion of the reaction (monitored by TLC), the reaction mixture was diluted with EtOAc and washed with water, brine and dried over Na2SO4. The solvent was evaporated and purified by silica gel column (60-120 mesh, elution 4% EtOAc in hexane) to afford title compound as a pale yellow syrup. Wt: 0.35 g; Yield: 51%; 1H NMR (300 MHZ, CDCl3): δ 7.39-7.28 (m, 5H), 5.12 (Brs, 2H), 4.60 (Brs, 1H), 3.88-3.79 (m, 1H), 2.65-2.53 (m, 1H), 2.38-2.27 (m, 1H), 2.01-1.99 (m, 1H), 1.43 (s, 9H), 1.28 (s, 3H), 0.86 (s, 3H); IR (KBr, cm−1): 3387, 2962, 1710, 1523, 1456, 1366, 1253, 1173, 1079, 1009, 979, 746, 698.
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