4-Bromophenylboronic Acid | CAS 5467-74-3 | ≥98%

4-Bromophenylboronic Acid (4-bromobenzeneboronic acid, p-bromophenylboronic acid) carries a para-bromine with σp +0.23, essentially matching para-chloro in Hammett electronic terms, and has a measured boronic-acid pKa around 8.2 in water at 25 °C, below phenylboronic acid (≈ 8.9). The aryl C–Br bond is a versatile downstream handle: more reactive than the corresponding aryl chloride in Pd-catalysed cross-coupling, accessible to halogen–metal exchange and magnesium insertion when the boron centre is suitably protected, and an AB-type aryl bromide / boronic-acid motif for Suzuki polycondensation or para-phenylene incorporation. Used as a 4-bromophenyl building block in medicinal chemistry, agrochemicals, conjugated materials, organic semiconductors, and polymer synthesis.

May contain small amounts of the cyclic anhydride 4-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: with aryl, heteroaryl, or alkenyl electrophiles to give 4-bromophenyl biaryls, heterobiaryls, terphenyls, and styrenyl products. Selectivity for the boronic acid over the aryl bromide depends on electrophile class and catalyst system; aryl iodide or aryl triflate partners typically allow the C–Br to be retained for later use.
• Iterative cross-coupling at the bromide handle: the C–Br bond can be engaged in subsequent Pd- or Ni-catalysed Suzuki–Miyaura, Buchwald–Hartwig, Negishi, Stille, Sonogashira, or Heck chemistry; relative to aryl chlorides, aryl bromides generally require less forcing oxidative-addition conditions, although catalyst and ligand choice remain coupling-class-dependent.
• Photoredox / nickel dual-catalysis cross-coupling: reported as the aryl bromide partner in Csp³–Csp² coupling with alkyltrifluoroborates; unprotected 4-bromophenylboronic acid is a specific example where the free boronic acid is tolerated as a latent functional group and remains available for subsequent Suzuki–Miyaura chemistry.
• Iron-catalysed radical arylation of arenes: reported in Fe(OTf)3 / 1,10-phenanthroline-mediated oxidative coupling with benzene derivatives using di-tert-butyl peroxide as oxidant; aryl radicals generated from the boronic acid undergo homolytic aromatic substitution to give 4-bromobiaryl products while retaining the para-bromide.
• Halogen–metal exchange and organomagnesium chemistry: the para-bromide can be converted to aryl-lithium or aryl-magnesium intermediates in protected boronate formats, with pinacol, MIDA, Bdan, or related protected boron derivatives preferred where the boron function must survive; the free boronic acid is not directly compatible with strong organolithium or Grignard conditions.
• Chan–Lam coupling: copper-mediated C–N and C–O arylation onto amines, amides, sulfonamides, carbamates, N–H heterocycles, phenols, and selected alcohols.
• Petasis borono-Mannich reaction: three-component coupling with an amine and a carbonyl partner to give α-aryl amines, α-amino acids, or β-amino alcohols bearing the 4-bromophenyl group, metal-free.
• Pd-catalysed Heck-type and conjugate addition chemistry: reported in stereoselective Heck-type arylation of allylic esters and Pd(II)-catalysed diastereoselective conjugate addition to activated alkenes.
• Tandem Pd(II) oxidative Heck / C–H amidation: reported in tandem-type oxidative Heck arylation followed by intramolecular C–H amidation sequences for heterocycle construction.
• Copper-mediated fluoroalkylation: reported in ligandless aerobic Cu-catalysed reactions with fluoroalkyl iodides to give 4-bromo-fluoroalkylarene products.
• AB-type Suzuki polycondensation: the bifunctional aryl bromide / boronic-acid pair makes the molecule an AB-type monomer or capping unit for poly(para-phenylene)-type and related Suzuki-polycondensation architectures.
• Protected boronate esters: precursor to pinacol (Bpin), neopentyl glycol, MIDA, and 1,8-diaminonaphthalene (Bdan) esters. Bdan masking is particularly useful in iterative synthesis, allowing Pd-catalysed reactions at the C–Br bond while the boron centre remains inert until later deprotection.
• Non-classical arylation: Suzuki–Miyaura-type coupling with arenediazonium tetrafluoroborates as alternative aryl electrophiles.
• Ipso-halodeboronation: deborylative bromination or iodination of arylboronic acids can replace the boronic-acid group with halogen; for the 4-bromo substrate this provides access to para-dihalogenated benzene motifs such as 1,4-dibromobenzene or 1-bromo-4-iodobenzene, depending on halogen source and conditions.
• Oxidative ipso-hydroxylation: peroxide- or perborate-mediated conversion to 4-bromophenol under mild arylboronic-acid hydroxylation conditions; aerobic photoredox and copper-catalysed variants are broader arylboronic-acid method classes.

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.