[C:1]([O:5][C:6]([NH:8][CH2:9][CH:10]([CH2:15][CH:16]([CH3:18])[CH3:17])[CH2:11][C:12]([OH:14])=[O:13])=[O:7])([CH3:4])([CH3:3])[CH3:2].C([O-])([O-])=O.[Cs+].[Cs+].[CH2:25](Br)[C:26]1[CH:31]=[CH:30][CH:29]=[CH:28][CH:27]=1>CN(C=O)C>[C:1]([O:5][C:6]([NH:8][CH2:9][CH:10]([CH2:15][CH:16]([CH3:18])[CH3:17])[CH2:11][C:12]([O:14][CH2:25][C:26]1[CH:31]=[CH:30][CH:29]=[CH:28][CH:27]=1)=[O:13])=[O:7])([CH3:4])([CH3:3])[CH3:2]To a stirred suspension of (37) (1.24 g, 4.78 mmol) and Cs2CO3 (1.56 g, 4.78 mmol) in DMF (20 mL) was added benzyl bromide (0.56 mL, 4.68 mmol). The resulting mixture was stirred at ambient temperature until the reaction was complete (˜2 h, as monitored by LC/MS). The mixture was poured into ice water and extracted with dichloromethane. The combined organic phase was washed with water and brine, then dried over anhydrous Na2SO4. Filtration and removal of the solvent in vacuo afforded the title compound (38) (1.77 g, 100%), which was used without further purification in the following example. 1H-NMR (CDCl3, 400 MHz): δ 0.86 (2 d, 6H), 1.13 (m, 2H), 1.42 (s, 9H), 1.62 (m, 1H), 2.31 (m, 2H), 3.00 (m, 1H), 3.18 (m, 1H), 4.75 (br.s, 1H), 5.10 (s, 2H), 7.33 (m, 5H). MS (ESI) m/z 372.30 (M+Na+).
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