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Example 5 Synthesis of 4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene: Cyclopentylbithiophene (1.5 g, 0.00843 mol) was dissolved in DMSO (50 mL). KOH (1.89 g, 0.0337 mol), sodium iodide (50 mg) and 2-ethylhexyl bromide (3.25 g, 0.0169 mol) were sequentially added to the solution under nitrogen protection. The reaction mixture was stirred under nitrogen atmosphere for 16 hours. After completion of the reaction, water was added and the reaction mixture was extracted with tert-butyl methyl ether. The organic layer was separated, dried with magnesium sulfate and concentrated. The residue was purified by column chromatography using hexane as eluent. The grades containing pure 4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene were combined and concentrated. After vacuum drying, a colorless oily product was obtained in a yield of 2.68 g (79%).1H NMR (CDCl3, 250 MHz): δ 7.13 (m, 2H), 6.94 (m, 2H), 1.88 (m, 4H), 0.94 (m, 16H), 0.78 (t, J=6.4 Hz, 6H), 0.61 (t, J=7.3 Hz, 6H).