Triflic anhydride (0.23 mL, 1.4 mmol) was added to a mixture of 3-(4-chloro-phenyl)-but-3-en-2-one (189 mg, 1.04 mmol) and 2,6-di-t-butyl-4-methylpyridine (0.32 g, 1.6 mmol) in CH2Cl2 (10 mL) and refluxed for 16 h. After cooling to room temperature, the solution washed with 10% HCl solution and saturated NH4Cl aqueous solution, dried (MgSO4), concentrated, and chromatographed (SiO2, hexanes) to give trifluoro-methanesulfonic acid 2-(4-chloro-phenyl)-1-methylene-allyl ester as a clear oil (136 mg, 41%).
