4-Nitrophenylboronic Acid | CAS 24067-17-2 | ≥97%

4-Nitrophenylboronic Acid (4-nitrobenzeneboronic acid, p-nitrophenylboronic acid) is a highly electron-deficient arylboronic acid generally used as a building block in medicinal chemistry, agrochemical development, and the synthesis of electron-poor π-conjugated materials. The presence of the para-nitro group strongly withdraws electron density from both the aromatic ring and the boronic-acid center (σp = +0.78). This extreme electron withdrawal gives the compound an unusually low pKa of approximately 7.1—well below that of standard phenylboronic acid (≈ 8.8)—ensuring that substantial boronate fraction exists even at near-neutral pH. Notably, while it possesses high Lewis acidity, its rate of protodeboronation is dictated by the full substitution pattern rather than pKa alone. Beyond its role as an aryl-transfer reagent, the nitro group provides a valuable orthogonal handle post-coupling; it can be readily reduced to an aniline derivative, unlocking a vast array of downstream transformations via diazonium chemistry.

May contain small amounts of the cyclic anhydride 4-nitrophenylboroxine. 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, and alkenyl electrophiles to give 4-nitrobiaryls and related products. Ligand-free Pd-catalysed protocols are reported.
• Nitro group transformations: the para-nitro group is an orthogonal handle on the coupled biaryl. Catalytic hydrogenation or chemical reduction (Sn/HCl, Fe/HCl, Zn, SnCl2) gives the 4-aminobiaryl; partial reduction gives nitroso, hydroxylamine, or azo intermediates. The aniline allows accessing Sandmeyer chemistry — halides, phenols, cyanides, fluorides (Balz–Schiemann), azides, and arenes.
• Lewis acidity and Hammett reference: σp(NO2) = +0.78 and pKa ≈ 7.1 place 4-nitrophenylboronic acid at the electron-poor end of common arylboronic acids — useful for comparing substituent effects on ionisation.
• Petasis borono-Mannich: metal-free three-component coupling with amine and carbonyl partners gives α-(4-nitrophenyl) amines, amino acids, or β-amino alcohols.
• Rhodium-catalysed 1,4-addition: a heterogeneous Rh-grafted hydrotalcite catalyst performs achiral 1,4-addition of organoboron reagents to electron-deficient olefins. Homogeneous chiral Rh systems with chiral diene or BINAP ligands extend the same chemistry to enantioselective conjugate addition.
• Palladium-catalysed direct arylation: the 4-nitroaryl source in Pd-catalysed C–H arylation of arenes and heteroarenes.
• Tandem Pd sequence: regioselective Suzuki–Miyaura followed by tandem Pd(II) intramolecular aminocarbonylation/annulation, giving N-heterocycles with a 4-nitroaryl substituent.
• Ruthenium-catalysed direct arylation: reported for benzylic sp3 C–H arylation of acyclic amines using a pyridyl directing group, giving α-(4-nitroaryl) amines.
• Copper-catalysed Chan–Lam N-arylation of ureas: Cu(acac)2-catalysed N-arylation of phenylurea and related ureas, giving 4-nitroaryl ureas.
• Copper-mediated cyanation: Cu-mediated conversion of arylboronic acids to aryl nitriles. For this substrate, gives 4-nitrobenzonitrile — a precursor to tetrazoles, amidines, and primary amides.
• Regioselective glycosylation of unprotected sugars: Tanaka and co-workers report 4-nitrophenylboronic acid as a catalyst for regio- and 1,2-cis-stereoselective SNi-type glycosylation of 1,2-anhydro donors with unprotected sugar acceptors in water. Reversible boronate formation with cis-diols on the acceptor directs the glycosylation site — the compound acts as a diol-recognition catalyst rather than as an aryl-transfer reagent.
• Protected boronate esters: precursor to Bpin, neopentyl glycol, MIDA, and Bdan esters for iterative cross-coupling and easier chromatography.
• Non-classical arylation: coupling with arenediazonium tetrafluoroborates as alternative aryl electrophiles.
• Ipso-halodeboronation: arylboronic-acid halodeboronation methods can replace B(OH)2with Br, Cl, or I, giving access to para-halonitrobenzene motifs such as 4-bromo-, 4-chloro-, or 4-iodonitrobenzene depending on the halogen source and conditions.
• Oxidative ipso-hydroxylation: peroxide or perborate gives 4-nitrophenol under mild conditions; Cu/aerobic and Fe-mediated variants offer alternative oxidants.

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.