Titanium(IV) chloride and oxy-compounds promoted Baylis–Hillman reaction

The Baylis–Hillman reaction of aryl aldehydes with α,β-unsaturated ketones in the presence of titanium(IV) chloride can be promoted by oxy-compounds at room temperature, although they are not as effective as amines, chalcogenides, or quaternary ammonium salts. The oxy-compounds can be simple alcohols, ethers, and ketones. For aryl aldehydes having a strong electron-withdrawing group on the phenyl ring such as nitrobenzaldehyde or p-trifluoromethylbenzaldehyde, the chlorinated compound 1 is obtained as the major product. However, for other aryl aldehydes, the elimination compound 3 was formed predominantly. We also found that TiCl4·2THF or TiCl4·2Et2O complex is very effective for this reaction to give the chlorinated products in high yields at low temperature. A plausible mechanism is proposed.