4-Fluorophenylboronic Acid | CAS 1765-93-1 | ≥98%

4-Fluorophenylboronic Acid (4-fluorobenzeneboronic acid, p-fluorophenylboronic acid) carries a para-fluorine with a modest net electron-withdrawing effect (σp ≈ +0.06): strong −I withdrawal is partly offset by weak +M donation from the fluorine lone pairs. In products derived from this reagent, the aryl C–F tunes lipophilicity, metabolic stability, dipole, conformational preference, π-stacking, and molecular recognition, and provides a built-in 19F NMR handle for tracking the boronic acid, its esters, and its binding partners in solution. It is used as a building block in medicinal chemistry, agrochemicals, natural-product analogues, fluorinated π-conjugated materials, and liquid-crystal precursors.

Like many arylboronic acids, this material may contain small amounts of the corresponding cyclic anhydride, 4-fluorophenylboroxine. Under aqueous or basic coupling conditions the two forms re-equilibrate and the practical impact on yield is minor.

Applications and Reactions

• Suzuki–Miyaura coupling: with aryl, heteroaryl, or alkenyl electrophiles to give 4-fluorophenyl-substituted biaryls, heterobiaryls, terphenyls, and styrenyl products. Widely used in SAR work and materials synthesis.
• Chan–Lam coupling: copper-mediated C–N and C–O arylation, transferring the 4-fluorophenyl group to amines, amides, sulfonamides, carbamates, N–H heterocycles, phenols, and selected alcohols.
• Rhodium-catalysed 1,4-addition: conjugate addition to α,β-unsaturated carbonyls and related activated alkenes. Chiral ligand systems give enantioenriched β-(4-fluorophenyl) carbonyl products; chromone-type acceptors have been reported in good yield and high ee.
• Petasis borono-Mannich reaction: three-component condensation with an amine and a carbonyl partner to give α-aryl amines bearing the 4-fluorophenyl group, under metal-free C–C/C–N bond-forming conditions.
• Diol recognition and saccharide sensing: forms reversible boronate esters with cis-1,2- and 1,3-diols. The mildly electron-withdrawing fluorine lowers the boronic-acid pKa relative to phenylboronic acid, improving boronate formation under near-neutral aqueous conditions.
• 19F NMR studies: the aryl fluorine gives distinct 19F chemical shifts for the free boronic acid, the boronate, and the diol ester, allowing each form to be followed directly in solution.
• Materials and liquid-crystal precursors: 4-fluorophenyl source for fluorinated biaryl, terphenyl, aryl–heteroaryl, chromophore, ligand, liquid-crystal, and functional-molecule intermediates.
• Non-classical arylation: coupling with arenediazonium tetrafluoroborates, diaryliodonium salts, and other hypervalent iodine reagents for installation of the 4-fluorophenyl group.
• Protected boronate ester synthesis: precursor to pinacol (Bpin), neopentyl glycol, and MIDA esters when a more robust 4-fluoroaryl-boron building block is required.
• Ipso-halodeboronation: conversion to 1-bromo-4-fluorobenzene, 1-chloro-4-fluorobenzene, or 1-fluoro-4-iodobenzene under appropriate electrophilic halogenation conditions.
• Oxidative hydroxylation: conversion to 4-fluorophenol under aerobic photoredox, peroxide-mediated, or copper-catalysed conditions.

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.