C[Li].Br[C:4]1[CH:5]=[C:6]([CH:9]=[CH:10][CH:11]=1)[NH:7][CH3:8].C([Li])(C)(C)C.[B:17](OC)([O:20]C)[O:18]C.Cl>C(OCC)C.O1CCCC1>[CH3:8][NH:7][C:6]1[CH:5]=[C:4]([B:17]([OH:20])[OH:18])[CH:11]=[CH:10][CH:9]=1
166 mL (0.242 mol, 1.2 eq) of 1.6 M methyllithium in diethyl ether are added to a solution cooled to −70° C. of 37.6 g (0.202 mol, 1 eq) of 3-bromo-N-methylaniline (prepared in Example 7c) in 300 ml of tetrahydrofuran. The reaction medium is stirred at −70° C. for one hour and 306 mL (0.444 mol, 2.2 eq) of 1.5 M tert-butyllithium in diethyl ether are then added. The reaction medium is stirred at −70° C. for 45 minutes and 103.5 mL (0.808 mol, 4 eq) of trimethyl borate are then added. The reaction medium is stirred at room temperature for one hour and then hydrolyzed by addition of ice, acidified with 1 L of 2N hydrochloric acid and extracted with ethyl acetate. The organic phases are combined, washed with water and dried over magnesium sulfate. The solvent is evaporated off and 4.2 g (14%) of 3-(methylamino)phenylboronic acid are obtained. The aqueous phase is basified and extracted with ethyl acetate. The organic phases are combined, washed with water and dried over magnesium sulfate. The solvent is evaporated off and the residue is chromatographed on silica gel (8/2 heptane/ethyl acetate). 3.4 g (11%) of 3-(methylamino)phenylboronic acid are obtained.
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