Syntheses of E- and Z-2- and 4-fluorourocanic acids

Horner–Wadsworth–Emmons olefination of ring-fluorinated N-trityl-imidazole carboxaldehydes with dialkyphosphonoacetic acid esters produced ring-fluorinated imidazolyl-E- and Z-acrylate esters. Stereochemistry was controlled by choice of phoshonate. Acid catalyzed removal of trityl followed by ester saponification gave the target 2- and 4-fluoro-E- and Z-urocanic acid derivatives. These are being investigated as potential mediators of photo-immunosupression.