BrC1[CH:3]=[C:4]([CH2:8][NH2:9])C=CC=1.[CH3:10][Li].[C:12]([Li])([CH3:15])([CH3:14])C.[B:17](OC)([O:20]C)[O:18]C.Cl>O1CCCC1>[CH3:10][NH:9][C:8]1[CH:4]=[C:3]([B:17]([OH:20])[OH:18])[CH:15]=[CH:12][CH:14]=1
37.6 g (202 mmol, 1 eq) of (3-bromophenyl)methylamine (obtained as in 1c) are dissolved in 300 mL of tetrahydrofuran. The reaction mixture is cooled to −70° C. and 166 mL (242 mmol, 1.2 eq) of 1.5 M methyllithium are then added slowly, while keeping the temperature at −70° C. The reaction mixture is stirred for 1 hour at −70° C. 306 mL (444 mmol, 2.2 eq) of 1.46 M tert-butyllithium are added, while keeping the temperature at −70° C. The reaction mixture is stirred for 45 minutes at −70° C. 103.5 ml (808 mmol, 4 eq) of trimethyl borate are added at −65° C. and the reaction mixture is then warmed to room temperature. The reaction is stopped by adding 1 L of 1N hydrochloric acid. The pH is adjusted to pH 5 and the reaction medium is then extracted with n-butanol. The organic phases are combined and dried over sodium sulfate. The solvents are evaporated off and the residue is then chromatographed on silica gel (70/30 heptane/ethyl acetate). 11.3 g of N-methyl-3-aminophenylboronic acid are obtained. Yield=40%.
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