[O:1]1[CH2:5][CH2:4][CH2:3][CH2:2]1.[CH2:6]([Li])[CH2:7][CH2:8][CH3:9].[B:11]([O:16]C)(OC)[O:12]C.Cl>CCCCCC>[CH:6]1[C:3]2[C:4]3[CH:2]=[CH:3][CH:4]=[CH:5][C:5]=3[O:1][C:2]=2[CH:9]=[CH:8][C:7]=1[B:11]([OH:16])[OH:12]Into a 500-mL three-neck flask was put 5.0 g (17 mmol) of 2-iodedibenzofuran, and the air in the flask was replaced with nitrogen. Into this flask was added 150 mL of tetrahydrofuran (THF), and this solution was cooled to −80° C. Then, 13 mL (20 mmol) of n-butyllithium (a 1.6 mol/L hexane solution) was dripped into this solution with a syringe. After the dripping, this solution was stirred at the same temperature for 1 hour. After the solution was stirred, to this solution was added 2.8 mL (25 mmol) of trimethyl borate, and the mixture was stirred for about 15 hours while the temperature of the mixture was being brought back to room temperature. After the stirring, about 50 mL of dilute hydrochloric acid (1.0 mol/L) was added to this solution, followed by stirring for 1 hour. After the stirring, the aqueous layer of this mixture was extracted with ethyl acetate, and the solution of the extract was combined with the organic layer, and washed with a saturated aqueous solution of sodium hydrogen carbonate and saturated brine. The organic layer was dried with magnesium sulfate. After the drying, the mixture was filtered. The obtained filtrate was concentrated, so that a pale brown solid was obtained. This solid was recrystallized with toluene/hexane to give 2.0 g of a white powder, which was the objective substance, in 55% yield. The synthesis scheme of Step 2 is shown in (a-2).
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