Br[C:2]1[CH:14]=[CH:13][C:5]2[O:6][C:7]3[CH:12]=[CH:11][CH:10]=[CH:9][C:8]=3[C:4]=2[CH:3]=1.C([Li])CCC.[B:20](OC)([O:23]C)[O:21]C.Cl>CCCCCC.C1COCC1>[CH:3]1[C:4]2[C:8]3[CH:9]=[CH:10][CH:11]=[CH:12][C:7]=3[O:6][C:5]=2[CH:13]=[CH:14][C:2]=1[B:20]([OH:23])[OH:21]Under an argon atmosphere, 24.7 g of 2-bromodibenzofuran and 400 ml of anhydrous THF were loaded into a 1,000-ml three-necked flask, and then 63 ml of a solution of n-butyllithium in hexane having a concentration of 1.6 M were added to the mixture during the stirring of the mixture at −40° C. The reaction solution was stirred for 1 hour while being heated to 0° C. The reaction solution was cooled to −78° C. again, and then a solution of 26.0 g of trimethyl borate in 50 ml of dry THF was dropped to the solution. The reaction solution was stirred at room temperature for 5 hours. 200 milliliters of 1N hydrochloric acid were added to the solution, and then the mixture was stirred for 1 hour. After that, the aqueous layer was removed. The organic layer was dried with magnesium sulfate, and then the solvent was removed by distillation under reduced pressure. The resultant solid was washed with toluene. Thus, 15.2 g of dibenzofuran-2-boronic acid were obtained.
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