Imitrodast can be obtained by two related ways: 1) The carboxylation of 4,5,6,7-tetrahydrobenzo[b]thiophen-7-one (I) with dimethyl carbonate by means of NaH in DMF gives 7-oxo-4,5,6,7-tetrahydro[b]thiophene-6-carboxylic acid methyl ester (II) (1, 2), which is reduced with NaBH4 and dehydrated with p-toluenesulfonic acid yielding 4,5-dihydrobenzo[b]thiophene-6-carboxylic acid methyl ester (III). The formylation of (III) with dichloromethyl methyl ether and AlCl3 in methylene chloride affords the corresponding 2-formyl derivative (IV), which is reduced with NaBH4 in methanol/THF to the hydroxymethyl derivative (V). The reaction of (V) with SOCl2 in dichloromethane gives the chloromethyl derivative (VI), which is condensed with the sodium derivative of imidazole (VII) by means of 4-(dimethylamino)pyridine in dichloromethane yielding 2-(1-imidazolylmethyl)-4,5-dihydrobenzo[b]thiophene-6-carboxylic acid methyl ester (VIII). Finally, this compound is hydrolyzed with NaOH in aqueous ethanol.
2) The formylation of 4-(3-thienyl)butyric acid ethyl ester (IX) with dichloromethyl methyl ether and SnCl4 in dichloromethane gives 4-(2-formylthien-3-yl)butyric acid ethyl ester (X), which is cyclized with sodium ethoxide (NaH/ethanol) in hot toluene yielding 4,5-dihydrobenzo[b]thiophene-6-carboxylic acid ethyl ester ester (XI).