4-Formylphenylboronic Acid | CAS 87199-17-5 | ≥98%

4-Formylphenylboronic acid (4-boronobenzaldehyde; 4-(dihydroxyboryl)benzaldehyde; p-formylphenylboronic acid) is a bifunctional arylboronic acid carrying a formyl (aldehyde) group para to the boronic acid.

May contain small amounts of the cyclic anhydride 4-formylphenylboroxine. Under aqueous or basic coupling conditions the two forms re-equilibrate and the impact on yield is minor.

Orthogonal bifunctionality: the molecule carries two independent handles — a boronic acid for C–C cross-coupling and a para-aldehyde for C–N and C=C bond formation. The aldehyde is compatible with standard Suzuki conditions and survives the coupling intact, so the two groups can be addressed sequentially, allowing modular assembly from a single compact reagent.

Applications and Reactions

• Suzuki–Miyaura cross-coupling: installs the 4-formylphenyl group into biaryls and heteroaryls bearing a free aldehyde, with couplings proceeding even in aqueous media. The retained aldehyde is then a handle for reductive amination, imine (Schiff-base) condensation, Wittig olefination, or oxidation to the carboxylic acid.
• Ketone synthesis and oxidative coupling: palladacycle-catalysed cross-coupling with carboxylic anhydrides or acyl chlorides gives aryl ketones; the compound also serves as the aryl nucleophile in palladium-catalysed aerobic oxidative cross-coupling.
• Copper-mediated ipso-functionalisation: ligandless aerobic fluoroalkylation with fluoroalkyl iodides replaces the boron with a perfluoroalkyl chain to give 4-(perfluoroalkyl)benzaldehydes; copper-catalysed ipso-nitration gives 4-nitrobenzaldehyde; and ligand-free copper-catalysed coupling with nitroarenes furnishes unsymmetrical diaryl ethers (C–O bond, the oxygen derived from water).
• Hantzsch multicomponent synthesis: in triethylamine-catalysed three-component Hantzsch condensations the aldehyde acts as the carbonyl component while the boronic acid is left free for a later cross-coupling — a one-pot route to dihydropyridine libraries that exploits both handles.
• Pharmaceutical building block: a Suzuki building block for biaryl pharmaceutical intermediates, including the angiotensin-II (AT1) receptor antagonist telmisartan.
• Serine-enzyme binding — β-lactamase inhibition and enzyme stabilisation: like other arylboronic acids it reversibly engages the catalytic serine of serine hydrolases. It is a documented reversible inhibitor of the class C enzyme AmpC β-lactamase in antibiotic-resistance research, and is used industrially to stabilise proteases and lipases in liquid-detergent formulations.
• Biosensors and surface functionalisation: the two handles are used together in sensor construction — the aldehyde binds covalently to amine-functionalised surfaces by Schiff-base condensation, while the boronic acid provides the diol-recognition element for saccharides (glucose, fructose) and catecholamines. It is used to build boronic-acid self-assembled monolayers on electrodes and to functionalise magnetic nanoparticles for catecholamine capture.
• Dye-sensitised solar cells: used to prepare push–pull sensitisers bearing dithiafulvenyl electron-donor units, where the aldehyde provides a condensation/anchoring point and the boronic acid enables Suzuki attachment to the conjugated chromophore for electron injection into TiO₂ photoanodes.
• Oxidative ipso-hydroxylation: oxidation of the C–B bond replaces boron with a hydroxyl to give 4-hydroxybenzaldehyde.

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.