1-(1′-Acetyl-5-mercaptospiro[indoline-3,3′-pyrrolidin]-1-yl)-2,2,2-trifluoroethanone (26 mg, 0.076 mmol) was dissolved in dimethylformamide (1 mL). Thereafter, potassium carbonate (32 mg, 0.23 mmol) and cyclopentane bromide (23 mg, 0.15 mmol) were added to the above obtained solution, and the thus obtained mixture was then stirred at room temperature for 1.5 hours. Thereafter, the reaction solution was diluted with water, and was then extracted with ethyl acetate. The organic layer was washed with brine, and was then dried over anhydrous magnesium sulfate, followed by concentration in vacuo. The obtained residue was purified by preparative thin-layer chromatography (chloroform:methanol=20:1) to obtain 1-(1′-acetyl-5-(cyclopentylthio)spiro[indoline-3,3′-pyrrolidin]-1-yl)-2,2,2-trifluoroethanone (13 mg, 42%) in the form of a colorless oily product.
