Treatment of 3,4-methylenedioxycinnamic acid (I) with thionyl chloride and pyridine gives the benzothiophene-2-carbonyl chloride (II), which is reacted with methanol in toluene to produce the methyl ester (III). Cleavage of the methylenedioxy group of (III) with BBr3 affords the dihydroxy derivative (IV), which upon alkylation with 4-(phenylsulfanyl)benzyl chloride (V) yields the diether derivative (VI). The ester function of (VI) is then reduced by LiAlH4 to the primary alcohol (VII), which is further oxidized to aldehyde (VIII) by means of MnO2 in toluene. Substitution of the chlorine atom of (VIII) with 4-chlorophenol (IX) in the presence of NaH furnishes the chlorophenyl ether (X).

Knoevenagel condensation of aldehyde (X) with ethyl pyridylacetate (XI) in the presence of Ac2O leads to the unsaturated ester (XII), which is finally submitted to saponification with ethanolic NaOH to furnish the corresponding carboxylic acid.