(Methoxymethyl)triphenylphosphonium chloride (0.63 g, 1.85 mmol) was dissolved in tetrahydrofuran (4 mL). Thereafter, potassium tert-butoxide (0.21 g, 1.85 mmol) was added to the above obtained solution under cooling on ice, and the thus obtained mixture was then stirred for 10 minutes. Thereafter, a tetrahydrofuran solution (3 mL) of the 1′-acetyl-N-(5-chlorothiazol-2-yl)-5-formylspiro[indoline-3,3′-pyrrolidine]-1-carboxamide (100 mg, 0.247 mmol) obtained in Step 2 of Example 401 was added to the reaction solution, and the thus obtained mixture was then stirred at room temperature for 1 hour. Thereafter, a saturated aqueous solution of ammonium chloride and water were added to the reaction solution, and the mixed solution was then extracted with ethyl acetate. 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 (chloroform:methanol=30:1) to obtain 1′-acetyl-N-(5-chlorothiazol-2-yl)-5-(2-methoxyvinyl)spiro[indoline-3,3′-pyrrolidine]-1-carboxamide (83 mg, 78%) in the form of a yellow amorphous product.
