*3.6. General Procedure of Dehydration under Acidic Conditions* (**3aa, 3da-dd**)

To a stirred solution of the corresponding alcohol **8** (0.20 mmol) in CH2Cl2 (2.4 mL) was added trifluoroacetic acid (TFA) (0.3 mL) at rt. After 1 h, volatile material was distilled off under reduced pressure. The crude residue was purified by column chromatography to afford 3-(1,3-diarylallyliden)oxindole **3**.
