3-(1,3-Dithian-2-ylidene)-2,4-pentanedione

Typical procedure (Entry 1 : R¹ = 4-MeO-Ph, R² = H ) :
3-(1,3-Dithian-2-ylidene)-2,4-pentanedione 1 (10 mmol), 4-methoxybenzaldehyde (10 mmol), and concd aq HCl (10 mmol) are added to a flask in a water bath. The mixture is heated to 60 °C under stirring. After the reaction is completed, within 15 min as indicated by TLC, the reaction mixture is cooled down to r.t. and neutralized with 10% aq NaHCO₃ (10 mL). The solid product is collected by filtration and washed with H₂O (3 × 30 mL). Further purification is carried out by silicagel flash column chromatography (petroleum ether/ethyl acetate = 75/1) to give 2-(4-methoxyphenyl)-1,3-dithiane in 97% yield as a white solid.