3,3′-dibromo-5,5′-bis(trimethylsilyl)-2,2′-bithiophene (Compound E4, synthesized in accordance with WO 2010/136353, 5.0 g) was placed in a 200 mL four-necked flask in a nitrogen atmosphere, and dissolved in tetrahydrofuran (75 mL). This was cooled to −78° C., and a solution of n-butyl lithium in hexane (KANTO CHEMICAL CO., INC., 1.64 M, 13.7 mL) was added dropwise. After about 30 minutes of agitation, the dichlorodi-n-decylsilane (Compound E21) (4.89 g) synthesized in Synthesis Example A19 was added dropwise. The temperature was gradually raised to room temperature over the course of about 2 hours, after which water was added, and the product was extracted with hexane. The organic layer was washed with water, dried with anhydrous sodium sulfate, and concentrated by filtration. The resulting yellow-orange oily substance was dissolved in hexane (50 mL) and chloroform (25 mL), trifluoroacetic acid (2.2 mL) was added with the internal temperature at 2° C., and after 10 minutes of agitation water was added, and the organic layer was washed, dried with anhydrous sodium sulfate and then and concentrated by filtration. Heptane (32 mL) was added to the reaction solution, which was then concentrated under reduced pressure. The resulting yellow-green oily substance was dissolved in hexane, and subjected to silica gel column chromatography (solvent: hexane) to obtain the target 4,4-di-n-decyl-dithieno[3,2-b:2′,3′-d]silole (Compound E22, 4.46 g, yield 88%).
