[CH2:1]([O:3][C:4]1[C:12]2[S:11][CH:10]=[CH:9][C:8]=2[C:7]([O:13][CH2:14][CH3:15])=[C:6]2[S:16][CH:17]=[CH:18][C:5]=12)[CH3:2].C([Li])CCC.CCCCCC.[CH3:30][Sn:31](Cl)([CH3:33])[CH3:32].CCOCC>C1COCC1.CCCCCC.O>[CH2:14]([O:13][C:7]1[C:6]2[S:16][C:17]([Sn:31]([CH3:33])([CH3:32])[CH3:30])=[CH:18][C:5]=2[C:4]([O:3][CH2:1][CH3:2])=[C:12]2[S:11][C:10]([Sn:31]([CH3:33])([CH3:32])[CH3:30])=[CH:9][C:8]=12)[CH3:15]To a solution of 556 mg (2.0 mmol) of 4,8-diethoxythieno[2,3-f]benzothiophene (26) in 8 ml of dry THF are added dropwise 1.6 ml (4.1 mmol) of 2.5 M n-butyllithium/hexane solution at −78° C. After the mixture has been stirred at −78° C. for 1 h, the cooling bath is removed and the mixture is stirred at room temperature for a further hour. The mixture is cooled to −78° C. and a solution of 4.2 ml (4.2 mmol) of 1.0 M trimethylstannyl chloride in n-hexane is added. The reaction mixture is stirred at −78° C. for another 10 min and then at room temperature for 16 h. 20 ml of ether and 20 ml of water are added and the organic phase is separated. The aqueous phase is extracted with 20 ml of ether, and the organic phases are combined and dried over sodium sulfate. After the solvents have been distilled off, the residue is dried under reduced pressure. The crude product (1.13 g, 94%) is used in the next stage without further purification. 1H NMR (CDCl3): 7.51 ppm (s, 2H), 4.38 (qa, 4H), 1.50 (t, 6H), 0.45 (s. 18H).
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