3-Methylsulfanyl-5-trifluoromethyl-1,3-dihydro-indol-2-one → 5-(Trifluoromethyl)oxindole

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A solution of 3-(methylthio)-5-(trifluoromethyl)oxindole (Gassman PG, Cue BW, Luh T-Y, J. Org. Chem. 1977;42:1344-1348) (10 g, 40 mmol) in AcOH (100 mL) was heated under reflux with Zn dust (13.3 g, 0.2 mol) for 1 hour. The mixture was cooled and filtered, and the precipitate was washed with AcOH. The combined filtrates were evaporated under reduced pressure, and the residue was diluted with 1M aqueous ammonia to give 5-trifluoromethyloxindole [VII: R1 =5-CF3, R3 =H] (7.22 g, 90%); mp (aqueous EtOH) 188.5°-191° C. (lit. [Hardtmann GE, U.S. Pat. No. 4,160,032; Chem. Abstr. 1979;91:P107890w]; mp 188°-189° C.).

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