Acetic Acid → (5-Bromo-2-fluorophenyl)boronic acid
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Br[C:2]1[CH:7]=[C:6]([Br:8])[CH:5]=[CH:4][C:3]=1[F:9].[Mg].C[O:12][B:13](OC)[O:14]C.C(O)(=O)C>O1CCCC1.C(OCC)C.O>[OH:12][B:13]([OH:14])[C:2]1[CH:7]=[C:6]([Br:8])[CH:5]=[CH:4][C:3]=1[F:9]Br[C:2]1[CH:7]=[C:6]([Br:8])[CH:5]=[CH:4][C:3]=1[F:9].[Mg].C[O:12][B:13](OC)[O:14]C.C(O)(=O)C>O1CCCC1.C(OCC)C.O>[OH:12][B:13]([OH:14])[C:2]1[CH:7]=[C:6]([Br:8])[CH:5]=[CH:4][C:3]=1[F:9]A solution of 2,4-dibromofluorobenzene (12.7 g, containing 30% 3,4-dibromofluorobenzene) in dry tetrahydrofuran (THF) (10 ml) is added over 5 min to a stirred suspension of magnesium turnings (1.15 g) in dry THF (50 ml) under an atmosphere of nitrogen and cooled in a water bath. After 1 hour, when all the magnesium has reacted, this reagent is added over 20 min to a stirred solution of trimethoxyborane (7 ml) in dry diethyl ether (80 ml) under an atmosphere of nitrogen and cooled at -78° C. The mixture is stirred at -78° C. for a further 15 min. and glacial acetic acid (6 ml) added followed by water (50 ml). The mixture is warmed to room temperature, extracted with diethyl ether (×3), washed with water, dried and the solvent evaporated under reduced pressure. The residue is stirred with carbon tetrachloride (30 ml) and then cooled at 0° C. The crystals of dihydroxy-(5-bromo-2-fluorophenyl)-borane are filtered off and washed with a little carbon tetrachloride. Yield 2.8 g m.p.t. 173°-174° C.
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