To the mixture of 6-chlorooxindole (3.3 g, 20 mmol) (Crescent) and 5-(tert-butyl-dimethyl-silanyloxy)-3,3-dimethyl-pentanal (6.5 g, 26.6 mmol) in methanol (150 mL) was added a methanolic solution (25%, Aldrich) of sodium methoxide (10 g, 46 mmol) dropwise. The reaction mixture was stirred at room temperature for 10 min. The solvent was removed, and the residue was partitioned between ethyl acetate and water. The organic layer was separated, dried over Na2SO4, and concentrated. The residue was purified by chromatography (25-33% EtOAc in hexanes) to give E/Z-3-[5-(tert-butyl-dimethyl-silanyloxy)-3,3-dimethyl-pentylidene]-6-chloro-1,3-dihydro-indol-2-one as a off white solid (Yield 3.6 g, 46%).
