3-Bromophenylboronic Acid | CAS 89598-96-9 | ≥97%

3-Bromophenylboronic Acid (3-bromobenzeneboronic acid, m-bromophenylboronic acid) is a bifunctional arylboronic acid carrying both a boronic acid and an aryl bromide at meta positions on the same ring. The meta-Br substituent is inductively electron-withdrawing (Hammett σm ≈ +0.39), giving an estimated pKa value near 8.0 vs the parent phenylboronic-acid pKa value of 8.76. The two functional groups can be reacted sequentially by careful selection of catalyst, electrophile, and boron-masking strategy.

The product may contain small amounts of the cyclic anhydride 3-bromophenylboroxine; under aqueous or basic coupling conditions the two forms re-equilibrate and the impact on yield is minor.

Applications and Reactions

• Suzuki–Miyaura coupling at the boronic acid: couples with suitably chosen aryl and heteroaryl electrophiles under matched Pd/phosphine/base conditions to install a meta-bromoaryl group on the coupled scaffold. When the aryl bromide is intended for later use, catalyst and electrophile choice should be selected to avoid premature oxidative addition at the retained Ar–Br bond.
• Iterative cross-coupling using the retained aryl bromide: the meta-Ar–Br in a Suzuki product can be used in a second Pd-catalysed cross-coupling under matched conditions. In the reverse sequence, the boronic acid can first be masked as its anthranilamide (AAM) boronate; the AAM-protected boronyl group is inactive under Suzuki conditions, allowing coupling at the aryl bromide before deprotection reveals the boronic acid for the next step.
• Rh-catalysed asymmetric 1,4-addition: under Hayashi–Miyaura-type Rh(I)/chiral ligand catalysis, 3-bromophenylboronic acid can serve as the aryl donor in conjugate addition to α,β-unsaturated ketones, giving enantioenriched β-(3-bromoaryl) carbonyl products. The aryl bromide remains a useful handle for later cross-coupling when the selected conditions preserve it.
• Gold-salt-catalysed homocoupling: gold-catalysed homocoupling of arylboronic acids provides symmetrical biaryls; for 3-bromophenylboronic acid this gives access to the corresponding 3,3'-dibromobiphenyl framework from a single boronic-acid reagent.
• C–H functionalisation of quinones: under catalytic AgNO3 with K2S2O8 as oxidant at room temperature, 3-bromophenylboronic acid arylates quinone C–H positions through a radical pathway, giving meta-bromoaryl-substituted quinones without prior halogenation of the quinone substrate.

Further Reading

For boronic acids, boronic esters, protodeboronation, boroxine content, and Suzuki–Miyaura reagent selection, see NorrChemica's Lab Journal guide: Choosing Your Boron Source for Suzuki–Miyaura Coupling.