Into a 300-mL three-neck flask were put 2.3 g (9.4 mmol) of 3-bromo-9H-carbazole, 2.0 g (9.4 mmol) of dibenzofuran-2-boronic acid, and 0.42 g (1.4 mmol) of tris(2-methylphenyl)phosphine. To the mixture were added 30 mL of ethanol, 50 mL of toluene, and 10 mL (2.0 mol/L) of an aqueous solution of potassium carbonate. This mixture was stirred to be degassed while the pressure was reduced. To this mixture was added 63 mg (0.28 mmol) of palladium(II) acetate. This mixture was stirred at 90° C. for 5 hours, cooled to room temperature, and then left for 15 hours; accordingly, a brown solid was precipitated. The precipitated solid was subjected to suction filtration and then collected. The collected solid was dissolved in about 30 mL of hot toluene, and this solution was suction-filtered through Celite (produced by Wako Pure Chemical Industries, Ltd., Catalog No. 531-16855), alumina, and Florisil (produced by Wako Pure Chemical Industries, Ltd., Catalog No. 540-00135). The resulting filtrate was concentrated to give a white solid. This solid was recrystallized with toluene/hexane to give 0.87 g of white powder in 27% yield. The synthesis scheme of Step 3 is shown in (a-3).
