[F:1][C:2]([F:13])([F:12])[C:3]([NH:5][CH:6]1[CH2:10][CH2:9][NH:8][C:7]1=[O:11])=[O:4].C[Si](C)(C)[N-][Si](C)(C)C.[Li+].Cl[C:25]([O:27][CH2:28][C:29]1[CH:34]=[CH:33][CH:32]=[CH:31][CH:30]=1)=[O:26].Cl>O1CCCC1>[CH2:28]([O:27][C:25]([N:8]1[CH2:9][CH2:10][CH:6]([NH:5][C:3](=[O:4])[C:2]([F:1])([F:12])[F:13])[C:7]1=[O:11])=[O:26])[C:29]1[CH:34]=[CH:33][CH:32]=[CH:31][CH:30]=1To Intermediate 3 (3.5 g) in tetrahydrofuran (100 ml) at −70° C. was added lithium hexamethyldisilazide (20 ml). After ¼ h, benzyl chloroformate (2.8 ml) was added. The mixture was warmed to room temperature for 1 h and 1 M hydrochloric acid (25 ml) added. After extraction with ethyl acetate (3×25 ml), the combined extracts were washed with 2% ammonia solution, 2M hydrochloric acid and brine, then dried (MgSO4). After solvent removal, the white solid was recrystallised from ethyl acetate: hexane 5:1 to give the title compound (4.2 g), T.l.c. silica (18:2 ethyl acetate: methanol) Rf 0.7.
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