Synthesis of (2-bromo-thiophen-3-yl)-acetic Acid methyl ester (2)
1] To a solution at 0 °C with 3-thiopheneacetic acid (1.42 g, 10 mmol) and methanol (20 mL) add acetic acid (1 mL) slowly.
2] Dilute with toluene and wash with NaHCO3 (sat. aq.) until basic.
3] Dry with MgSO4, filter and concentrate.
4] Dissolve in 20 mL chloroform/acetic acid (1:1) and cool to 0 °C.
5] Add 1.78 g NBS (10 mmol)
6] After five hours dilute with toluene and wash with NaHCO3 (sat. aq.) until basic.
7] Dry with MgSO4, filter and concentrate.
8] Purify on flush column chromatography (toluene).
Synthesis of (3''-methoxycarbonylmethyl-[2,2';5',2'']terthiophen-3-yl)-acetic acid methyl ester (3)
1] Dissolve 2 (2.35 g 10 mmol) and 2,5-thiophenediboronic acid (0.781 g, 4.5 mmol) in 20 mL degassed toluene/methanol (1:1).
2] Add 4.14 g (30 mmol) K2CO3 and PEPPSI-Ipr (0.204 g, 0.30 mmol) to the solution and heat at 80 °C for 10 minutes.
3] Filter the reaction mixture on celite, dilute with toluene and wash with NaHCO3 (sat. aq.).
4] Dry with MgSO4, filter and concentrate.
5] Purify the crude reaction mixture on a reversed phase column (methanol/H2O 4:1, 0.05 % trifluoroacetic acid) to give the product.
Synthesis of (5,5''-dibromo-3''-methoxycarbonylmethyl-[2,2';5',2'']terthiophen 3-yl)-acetic acid methyl ester (4)
1] Add NBS (0.460 g, 2.04 mmol) to a solution of the trimer (3, 0.382 g, 0.973 mmol) in chloroform/acetic acid (1:1, 5 mL, 0 °C).
2] Stir for 4 hours before dilution with diethyl ether (20 mL)
3] Wash with NaHCO3 (sat. aq., 20 mL) and finally water (20 mL).
4] Dry with MgSO4, filter and concentrate.
5] Purify by flash column chromatography (toluene).
Synthesis of 4',3'''-bis-carboxymethyl-[2,2';5',2'';5'',2''';5''',2'''']quinquethiophene-5,5''''-dicarboxylic acid (p-FTAA) (5)
1] Add K2CO3 (4.14 g, 30 mmol), PEPPSI-IPr (0.204 g, 0.30 mmol) and 5-(dihydroxyboryl)-2-thiophenecarboxylic acid to a solution of 4 (5.50 g, 10 mmol) in degassed toluene/methanole (1:1, 30 mL).
2] Heat at 80 °C for 10 minutes
3] Add HCl (20 mL, 1 M, aq.) and collect the red precipitate
4] Dissolve the precipitate in boiling dioxane and filter it on celite followed by precipitation by addition of a small amount of water.
5] Dry the precipitate and add two equimolar amounts of NaOH (1 M, aq.)
6] The product is afforded by concentration or freeze drying.