[H-].[Na+].[Cl:3][C:4]1[C:9]([Cl:10])=[C:8]([O:11][CH3:12])[CH:7]=[CH:6][C:5]=1[SH:13].Br[CH:15]([CH:19]([CH3:21])[CH3:20])[C:16]([OH:18])=[O:17]>CN(C)C=O.O>[Cl:3][C:4]1[C:9]([Cl:10])=[C:8]([O:11][CH3:12])[CH:7]=[CH:6][C:5]=1[S:13][CH:15]([CH:19]([CH3:21])[CH3:20])[C:16]([OH:18])=[O:17]To 3.13 g of 99% sodium hydride under nitrogen at room temperature is added a solution of 12.26 g of 2,3-dichloro-4-methoxythiophenol in 100 ml of sieve-dried dimethylformamide over 2 minutes. The reaction is stirred for 12 minutes. A solution of 9.56 g of α-bromoisovaleric acid in 85 ml of dimethylformamide is added over 4 minutes. The reaction is stirred at room temperature for 3 hours, cooled in ice, diluted with 500 ml of water and filtered. The solution is cooled and acidified with 3N hydrochloric acid to give the product. The precipitate is filtered, washed with a small amount of water, dried and recrystallized from acetone-pentane to give 13.14 g of α-(2,3-dichloro-4-methoxyphenylthio)isovaleric acid as a white crystalline powder mp 176.5°-178.5°.
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