251-41-2

61676-62-8

924894-85-9

Thieno[3,2-b]thiophene (1.5 g, 10.70 mmol) was dissolved in tetrahydrofuran (25.5 mL) under nitrogen protection and cooled to -78 °C. A hexane solution of n-butyllithium (8.988 mL, 2.5 M, 22.47 mmol) was added slowly and the reaction was stirred for 20 minutes. Subsequently, the cooling bath was replaced with an ice bath and stirring was continued for 50 minutes. The resulting thick suspension was quenched by the addition of 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (4.181 g, 4.584 mL, 22.47 mmol). The reaction mixture was stirred overnight at room temperature and then quenched with saturated aqueous ammonium chloride solution. The reaction mixture was extracted with dichloromethane (2 x 100 mL) and the organic phases were combined, washed with brine and dried over anhydrous sodium sulfate. The organic solution was diluted with about 20 mL of ethyl acetate and slowly concentrated by rotary evaporator until the dichloromethane was completely removed. The resulting fine white crystals were collected by filtration, washed with heptane and dried under high vacuum to afford 4,4,5,5-tetramethyl-2-[5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)thieno[3,2-b]thiophen-2-yl]-1,3,2-dioxaborolan-2-yl (2.57 g, 6.554 mmol, yield 61.25%), a semi-white solid.1H NMR (400 MHz, CDCl3) δ 7.75 (s, 2H), 1.343 (s, 12H).