[H-].[Na+].[F:3][C:4]1[C:9]2[N:10]=[C:11]([SH:13])[S:12][C:8]=2[C:7]([F:14])=[CH:6][C:5]=1[F:15].Br[CH2:17][CH2:18][CH2:19][CH2:20][C:21]([O:23][CH2:24][CH3:25])=[O:22].Cl>CN(C=O)C.O>[CH2:24]([O:23][C:21](=[O:22])[CH2:20][CH2:19][CH2:18][CH2:17][S:13][C:11]1[S:12][C:8]2[C:7]([F:14])=[CH:6][C:5]([F:15])=[C:4]([F:3])[C:9]=2[N:10]=1)[CH3:25]Sodium hydride (60% in oil, 220 mg, 5.5 mmol) was suspended in DMF (2 ml) and the suspension was stirred on a water bath. To the suspension was added dropwise a solution of 4,5,7-trifluoro-2-mercaptobenzothiazole (1.1 g, 5 mmol) in DMF (5 ml) under ice cooling and the mixture was stirred for 30 min. at room temperature and then cooled on a water bath. To the cooled mixture was added dropwise a solution of ethyl 5-bromopentanoate (1.05 g, 5 mmol) in DMF (3 ml) and the mixture was stirred for 2 hours at room temperature. The resultant mixture was diluted with water, then acidified with 7% hydrochloric acid and extracted with ethyl acetate. The organic layer was washed with an aqueous saturated saline solution, dried and then evaporated. The resulting residue was purified on a silica gel column to give 5-(4,5,7-trifluorobenzothiazol-2-ylthio)pentanoic acid ethyl ester (1.1 g, 64%) as an oil.
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