New approach to the synthesis of 2,2′:5′,2"-terthiophene-5,5"-and 2,2′:5′,2":5",2"′-quaterthiophene-5,5"′-dicarboxylic acids

The reaction of bromosuccinimide with esters of 3-substituted 2,2'-bithiophene-5-carboxylic acids was used to obtain their 5'-bromo derivatives, which were further converted to esters of 3,3"-disubstituted 2,2':5',2":5",2"'-quaterthiophene-5,5'-dicarboxylic acids by heating in DMF with catalytic amounts of Pd(PPh3)(4). Ester of 3-decy1-2,2'-bithiophene-5-carboxylic acid was acylated at the C-5' position with lauroyl chloride in the presence of SnCl4, producing the respective ketone that was used in Vilsmeier-Haack reaction (DMF, POCl3). The 3-chloroacrylaldehyde derivative that was thus obtained was further used in reaction with ethyl thioglycolate in the presence of sodium ethoxide, giving ester of 3,3"-decyl-2,2':5',2"-terthiophene-5,5"-dicarboxylic acid. Alkaline hydrolysis of the obtained esters led to the corresponding 2,2':5',2":5",2"-quaterthiophene-5,5"- and 2,2':5',2"-terthiophene-5,5"-dicarboxylic acids.