Acetone → 2,6-Dichlorobenzylideneacetone

A round bottom flask equipped with magnetic stirrer and nitrogen inlet was charged with 2,6-dichlorobenzaldehyde (5.0 g, 28.57 mmol), acetone (42 ml, 0.571 mol) and water (20 ml). The mixture was cooled to 0° C. and a solution of sodium hydroxide (1.14 g, 28.57 mmol) in water (20 ml) was added drop wise during 1 hour to the vigorous stirred suspension. The reaction mixture was stirred for an additional 0.5 hour. The reaction mixture was concentrated in vacuo, poured onto 10% HCl (100 ml) and extracted with ethyl acetate (3×50 ml). Combined organic layers were dried over anhydrous sodium sulfate. The solvent was removed in vacuo and the residue was purified by flash chromatography over silica gel (350 g) (eluent: n-hexane/ethyl acetate 10:1) to afford 6.0 g (97% of theory) of (E)-4-(2,6-dichloro-phenyl)-but-3-en-2-one in form of a pale yellow oil.