*3.5. General Procedure of Aldol Reaction* (**8aa**, **8da-dd**)

To a stirred solution of the corresponding 3-methyleneoxindole **5** (0.20 mmol) in THF (2.0 mL) was slowly added *n*-butyllithium (2.5 M in hexane, 0.088 mL, 0.22 mmol, 1.1 equiv.) at −78 ◦C under argon atmosphere. After stirring for 1 h at the same temperature, the corresponding benzaldehyde (0.26 mmol, 1.3 equiv.) was added. After stirring for additional 1.5 h at −78 ◦C, the reaction mixture was diluted with sat. aq. NH4Cl (10 mL) and EtOAc (50 mL). The organic layer was separated, dried over Na2SO4, filtered, and concentrated under reduced pressure. The crude residue was purified by column chromatography to afford aldol adduct **8**.
