t-Butyl spiro[indoline-3,3′-pyrrolidine]-1′-carboxylate (10.0 g, 36.4 mmol) was dissolved in methylene chloride (73 mL). Thereafter, triethylamine (15.2 mL, 109 mmol) and N-[2-(trimethylsilyl)ethoxycarbonyloxy]succinimide (14.2 g, 54.8 mmol) were added to the above obtained solution under cooling on ice, and the thus obtained mixture was then stirred at room temperature for 22 hours. Thereafter, the reaction solution was diluted with water, and was then extracted with chloroform. The organic layer was washed with brine, and was then dried over anhydrous sodium sulfate, followed by concentration in vacuo. The obtained residue was purified by silica gel column chromatography (hexane:ethyl acetate=5:1) to obtain 1-(2-(trimethylsilyl)ethyl) 1′-tert-butyl spiro[indoline-3,3′-pyrrolidine]-1,1′-dicarboxylate (16.1 g, quant.) in the form of a light yellow oily product.
