Titanium-Mediated Direct Carbon—Carbon Double Bond Formation to α-Trifluoromethyl Acids: A New Contribution to the Knoevenagel Reaction and a High-Yielding and Stereoselective Synthesis of α-Trifluoromethylacrylic Acids.

An efficient strategy for a high-yielding and stereoselective synthesis of α-trifluoromethyl unsaturated carboxylic acids directly from the reactions of 3,3,3-trifluoropropanoic acid (CF3CH2COOH) with various aryl aldehydes in the presence of titanium tetrachloride (TiCl4) is reported here for the first time, which is a valuable expansion for the classical Knoevenagel reaction. Because these compounds may have potential applications in organic electronics and can be easily converted to the corresponding fluorinated alcohols and amino acids with excellent bioactivity, this route should be a good choice for the preparation of α-trifluoromethyl-containing derivatives.