1′-Acetyl-N-(5-chlorothiazol-2-yl)-5-formylspiro[indoline-3,3′-pyrrolidine]-1-carboxamide (7.6 mg, 0.0188 mmol) was dissolved in t-butanol (1.5 mL) and water (0.5 mL). Thereafter, 2-methyl-2-butene (52 μL, 0.50 mmol), sodium dihydrogen phosphate (14 mg, 0.113 mmol) and sodium chlorite (15 mg, 0.169 mmol) were added to the above obtained solution, and the thus obtained mixture was then stirred at room temperature for 3.3 hours. Thereafter, a saturated aqueous solution of ammonium chloride was added to the reaction solution, and the mixed solution was then extracted with chloroform:methanol=5:1. The organic layer was dried over anhydrous sodium sulfate, and was then concentrated in vacuo. The obtained residue was purified by silica gel column chromatography (chloroform:methanol=5:1) to obtain the captioned compound (6.9 mg, 87%) in the form of a white solid.
