A simple approach to the synthesis of ethyl 2-ethoxy-4-methoxy-6-perfluoroalkylbenzoates via acyclic precursors

The acyclic precursors, methyl 3-perfluoroalkyl-4-carboethoxy-5-ethoxy-6-(triphenylphosphoranylidene)hexa-2,4-dienoates 3a-c were obtained through the addition reaction of ethyl 3-ethoxy-4-(triphenylphosphoranylidene)but-2-enoate 1 with equally molar of methyl 2-perfluoroalkynoates 2a-c. Ethyl 2-ethoxy-4-methoxy-6-perfluoroalkylbenzoates 4a-c were synthesized with high yields via an intramolecular elimination of Ph3PO of 3a-c by heating in anhydrous benzene in a sealed tube. The structures of these compounds were confirmed by IR, MS, H-1, C-13 and F-19 NMR spectra, and elemental analyses. The reaction mechanisms were also proposed.