4-Methoxyphenylboronic Acid | CAS 5720-07-0 | ≥98%

4-Methoxyphenylboronic Acid (4-anisylboronic acid, p-anisylboronic acid, 4-methoxybenzeneboronic acid) bears a para-methoxy group, a strong resonance donor (+M effect; σp ≈ −0.27). It is used in medicinal-chemistry, agrochemical, natural-product-analogue, and π-conjugated materials synthesis.

Like many arylboronic acids, 4-methoxyphenylboronic acid may contain small amounts of the corresponding cyclic anhydride, 4-methoxyphenylboroxine, in the solid state. Under aqueous/basic coupling conditions, boronic acid and boroxine forms usually re-equilibrate, but even minor boroxine content can affect assay, effective stoichiometry, and reproducibility.

Applications and Reactions

• Suzuki–Miyaura coupling: Used with aryl, heteroaryl, or alkenyl electrophiles to prepare p-anisyl-substituted biaryls, heterobiaryls, and aryl–alkene products. The methoxy group gives an electron-rich aryl unit useful in SAR, materials, and synthetic-methodology work.
• Chan–Lam coupling: Common partner in copper-mediated C–N and C–O arylation. It transfers the p-anisyl group to amines, amides, sulfonamides, carbamates, N–H heterocycles, compatible phenols, and selected alcohols.
• Rhodium-catalysed conjugate addition: Participates in 1,4-addition to α,β-unsaturated carbonyl substrates, transferring the p-anisyl group to the β-position of enones, enoates, enamides, nitroalkenes, and related Michael acceptors. Suitable chiral ligand systems can give enantioenriched β-(p-anisyl) carbonyl and β-(p-anisyl)nitro products.
• Petasis borono-Mannich reaction: Combines with an amine and a carbonyl component in a multicomponent reaction to give substituted amines bearing the p-anisyl group at the α-position to nitrogen. Glyoxylic acid/glyoxylates and suitable α-hydroxy aldehydes give access to α-(p-anisyl)-α-amino acid derivatives and β-amino-alcohol scaffolds.
• Electron-rich materials and functional-molecule synthesis: Practical p-anisyl source for biaryl, aryl-heteroaryl, and arylated small-molecule intermediates used in materials, ligand, dye, natural-product-analogue, and functional-molecule R&D. The p-anisyl unit is a recurring donor fragment in push-pull chromophores, electron-rich π-conjugated systems, and arylated heterocycles.
• Latent phenol handle: The methoxy group can undergo demethylation (e.g. BBr3, etc) to generate the corresponding phenol
• Protected boronate ester preparation: Precursor for protected 4-methoxyphenylboronate esters such as pinacol, neopentyl glycol, and MIDA derivatives when a more stable p-anisyl-boron building block s required.
• Ipso-halodeboronation: Can be converted to 4-bromoanisole, 4-chloroanisole, or 4-iodoanisole under suitable electrophilic halogenation conditions where the boronic acid has served as a directing or coupling handle in earlier steps.
• Oxidative hydroxylation: Substrate for conversion to 4-methoxyphenol (mequinol) under aerobic photoredox, peroxide-mediated, or copper-catalysed boronic acid → phenol conditions.
• Diol recognition studies: Secondary cis-diol recognition motif in boronate-ester binding studies. The electron-donating methoxy group tends to raise boronic-acid pKa, so practical glucose/saccharide sensing is usually weaker than with more acidic or amine-appended boronic acid receptors.

Further Reading

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