3',4'-Dihydroxyacetophenone (I) was selectively alkylated at position 4' with alpha-bromo-2,6-difluorotoluene (II) in the presence of Li2CO3 in DMF. The resulting ether (III) was further alkylated with ethyl bromoacetate (IV) to give (V). Subsequent Horner-Emmons condensation of (V) with the phosphonoacetamide (VI) provided cinnamide (VII). The target carboxylic acid was then obtained by saponification of the ethyl ester of (VII) with NaOH.

Simultaneous bromination and esterification of 2'-hydroxyphenylacetic acid (I) using tetrabutylammonium tribromide in EtOH at r.t. afforded (II), which was O-alkylated with alpha-bromo-2,6-difluorotoluene (III) in the presence of K2CO3 in refluxing acetone to yield ether (IV). Subsequent Heck olefination of (IV) with diethyl crotonamide (V) in the presence of palladium acetate and tri-o-tolylphosphine provided cinnamide (VI). The target carboxylic acid was then obtained by saponification of the ethyl ester of (VI) with NaOH.