1-(2-(Trimethylsilyl)ethyl) 1′-tert-butyl 5-vinylspiro[indoline-3,3′-pyrrolidine]-1,1′-dicarboxylate (674 mg, 1.52 mmol) was dissolved in dioxane (15 mL). Thereafter, sodium periodate (1.30 g, 6.08 mmol), water (5 mL), 2,6-lutidine (0.35 mL, 3.01 mmol), and osmium tetroxide (1% t-butanol aqueous solution, 1 mL) were added to the above obtained solution under cooling on ice, and the thus obtained mixture was then stirred at the same temperature as above for 3 hours. Thereafter, an aqueous solution of sodium sulfite was added to the reaction solution, and the mixture 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 5-formylspiro[indoline-3,3′-pyrrolidine]-1,1′-dicarboxylate (553 mg, 82%) in the form of a light yellow solid.
