[C:1]1(=[O:10])[CH:9]2[CH:4]([CH2:5][CH2:6][CH2:7][CH2:8]2)[CH2:3][NH:2]1.C(N(CC)CC)C.[O:18](C(OC(C)(C)C)=O)[C:19]([O:21][C:22]([CH3:25])([CH3:24])[CH3:23])=O>O1CCCC1.CN(C)C1C=CN=CC=1>[C:22]([O:21][C:19]([N:2]1[CH2:3][CH:4]2[CH:9]([CH2:8][CH2:7][CH2:6][CH2:5]2)[C:1]1=[O:10])=[O:18])([CH3:25])([CH3:24])[CH3:23]To 3 (835 mg, 6 mmol) in suspension in tetrahydrofuran (7 mL) was successively added, under an argon atmosphere, 4-dimethylaminopyridine (18.3 mg; 0.15 mmol), triethylamine (0.84 mL; 6 mmol) and BOC2O (2.62 g; 12 mmol). The reaction mixture was stirred at room temperature for 3 days. The solvent was removed under vacuum. The residue was diluted with diethyl ether (20 mL) and washed with water (2×10 mL). The phases were separated, and the organic phase was dried over MgSO4 and concentrated. The crude oil was purified over silica gel chromatography (ether/heptane 1:1) to give 4 (986 mg; 4.1 mmol; 70%) as a white solid.
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