3-Furanboronic Acid | CAS 55552-70-0 | ≥97%

3-Furanboronic acid (furan-3-ylboronic acid, 3-furylboronic acid) is a five-membered heteroarylboronic acid where the relative positioning of boron center and ring oxygen prevents the α-carbanion stabilisation pathway operative for the 2-isomer which translates into slower aqueous protodeboronation and the absence of disproportionation cascade processes.

The product may contain small amounts of the cyclic anhydride furan-3-ylboroxine; under aqueous or basic coupling conditions the two forms re-equilibrate and the impact on yield is minor.

Applications and Reactions

• Suzuki–Miyaura coupling: couples with aryl and N-heteroaryl halides (pyridines, pyrimidines, quinolines) using Pd or Ni catalysis. Compatible with activated/unactivated chlorides and biodegradable aqueous solvent systems.
• Heteroaryl–heteroaryl coupling: couples with N-heteroaryl halides — including bromo- and chloropyridines, halopyrimidines, and bromoquinolines — under suitably chosen Pd or Ni conditions, supporting its use for constructing mixed five/six-membered heterobiaryl motifs common in pharmaceutical and agrochemical intermediates.
• Protodeboronation behaviour: furan-2-boronic acid undergoes high-concentration disproportionation near its pKa, sequentially forming difurylborinic acid and trifurylborane before protodeboronation. In 3-furanboronic acid, the β-positioned boron prevents the arrangement required for this cascade. Nevertheless, the compound remains condition-sensitive; pH, base, concentration, and temperature must still be carefully controlled to avoid protodeboronation.
• Ni-catalysed Suzuki coupling: substrate for Suzuki–Miyaura coupling in green solvents to construct N-heteroaryl–furan biaryls (e.g., 5-(furan-3-yl)pyrimidine from 5-bromopyrimidine). Compatible with aryl/heteroaryl halides and phenol-derived electrophiles (carbamates, sulfamates, pivalates).
• Diol recognition and enzyme immobilisation: forms reversible cyclic boronate esters with cis-1,2- and 1,3-diols and glycan motifs in aqueous solutions. Oxidative electropolymerisation of a uricase–furan-3-boronic acid adduct on a Pd-plated multiwalled-carbon-nanotube/Au electrode yields a bionanocomposite functioning as an amperometric uric-acid biosensor and a uric-acid/O₂ enzymatic biofuel cell bioanode.
• Chan–Lam N-arylation: acts as the boron coupling partner in Cu(II)-mediated N-arylation of NH-heterocycles, anilines, and amides under mild aerobic conditions. Requires standard substrate-specific screening.
• Petasis borono-Mannich: participates in three-component coupling with amines and aldehydes (or glyoxylic / α-hydroxy aldehydes) to yield arylated amines, α-amino acid derivatives, or β-amino alcohols. Requires substrate-specific screening for optimal furan-3-yl transfer.
• Ipso-substitution (halodeboronation and hydroxylation): the B(OH)₂ group undergoes oxidative replacement by halogens (Cl, Br, I) via N-haloimides, or by OH via peroxide oxidation, yielding 3-halo- or 3-hydroxyfurans. Careful screening is required, as the furan 2,5-positions are highly sensitive to electrophilic oxidation and halogenation.
• Protected boronate esters: the pinacol ester (CAS 248924-59-6) offers a stable format for handling and cross-coupling. Other slow-release strategies — like MIDA boronates and potassium organotrifluoroborates — improve chromatographic handling, shelf stability, and iterative controlled-release Suzuki–Miyaura couplings (requires confirmed substrate-specific preparation protocols).

Further Reading

For comprehensive protocols on boronic acids, esters, protodeboronation, boroxine content, and reagent selection, refer to NorrChemica's Lab Journal guide: Choosing Your Boron Source for Suzuki–Miyaura Coupling.