PPh3 promoted stereospecific synthesis of ethyl α-chloroacrylates from ethyl trichloroacetate and arylaldehydes

A coupling reaction between arylaldehydes and ethyl trichloroacetate is facilitated by PPh₃ under mild conditions to stereospecifically produce (Z)-ethyl α-chloroacrylates. This stereospecific coupling reaction only occurs when the arylaldehyde derivative has an electron-withdrawing substituent. On the other hand, when an electron-donating group is present in the aromatic ring, the aryldichloromethyl derivative is formed as the only product, even at low temperature. The stereospecificity in the coupling reaction was established based on the coupling constants ²J_CH and ³J_CH in the ¹³C NMR and crystal-X-ray analysis. From this data we propose that the formation of these compounds occurs through two intermediates initially formed by the reaction between the PPh₃ and ethyl trichloroacetate.