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(PPh 3 ) 4 . Ester of 3-decyl-2,2'-bithiophene-5-carboxylic acid was acylated at the С-5' position with lauroyl chloride in the presence of SnCl 4 , producing the respective ketone that was used in Vilsmeier–Haack reaction (DMF, POCl 3 ). 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.