[SH:1][CH2:2][C:3]([O:5][CH2:6][CH3:7])=[O:4].[H-].[Na+].[CH3:10][O:11][C:12]([C:14]1[C:19]([F:20])=[CH:18][C:17](Br)=[C:16]([NH2:22])[N:15]=1)=[O:13].CCOC(C)=O>CN(C=O)C>[CH3:10][O:11][C:12]([C:14]1[C:19]([F:20])=[CH:18][C:17]([S:1][CH2:2][C:3]([O:5][CH2:6][CH3:7])=[O:4])=[C:16]([NH2:22])[N:15]=1)=[O:13]A solution of ethyl mercaptoacetate (1.15 ml) in DMF (40 ml) was ice-cooled under argon, treated with sodium hydride (420 mg of a 60% dispersion in oil) and stirred until all was in solution (about 1 hour). The ester (a) (2.48 g) was added, the mixture allowed to warm to room temp. and stirred overnight. EtOAc (150 ml) was added, the solution washed with water (3×150 ml), dried and evaporated. Chromatography of the residue (40% EtOAc in hexane) gave an oil (1.7 g).
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