3-Chlorophenylboronic Acid | CAS 63503-60-6 | ≥98%

3-Chlorophenylboronic acid (3-chlorobenzeneboronic acid; m-chlorophenylboronic acid) is a meta-substituted arylboronic acid bearing a chloro substituent at the 3-position of the ring.

May contain small amounts of the cyclic anhydride 3-chlorophenylboroxine. Under aqueous or basic coupling conditions the two forms re-equilibrate and the impact on yield is minor.

Reactivity: the meta-chloro group is moderately electron-withdrawing and sterically unobtrusive. With no ortho substituent or ring heteroatom adjacent to boron, it sits with the parent and simple 3-/4-substituted phenylboronic acids at the slow end of the protodeboronation scale, away from the labile ortho-disubstituted, polyfluoro, and 2-heteroaryl classes. Its defining feature is bifunctionality: in a standard Suzuki coupling the boron reacts while the aryl C–Cl is retained as a second handle.

Applications and Reactions

• Suzuki–Miyaura cross-coupling and sequential functionalisation: installs the 3-chlorophenyl group into biaryls and heterobiaryls from aryl, heteroaryl, and vinyl halides or pseudohalides. The retained meta C–Cl bond then serves as an orthogonal handle for a second Suzuki coupling, Buchwald–Hartwig amination, or palladium-catalysed cyanation, giving stepwise access to polysubstituted biaryls and terphenyls from a single building block. It has also been coupled with dibromo(trifluoromethyl)benzene to give CF₃-substituted chlorobiphenyls.
• Pharmaceutical building block — vadadustat and PDE4 inhibitors: a documented building block in the synthesis of the HIF-prolyl-hydroxylase (HIF-PHD) inhibitor vadadustat, developed for anaemia of chronic kidney disease, where Suzuki coupling installs the 3-chlorophenyl group onto the pyridine core. It is also used to introduce the 3-chloroaryl fragment into PDE4 (phosphodiesterase-4) inhibitor scaffolds.
• Biaryl ketones and phthalides: carbonylative Suzuki coupling under carbon monoxide gives biaryl ketones; the compound is also used in the synthesis of phthalide (isobenzofuran-1(3H)-one) scaffolds.
• 1,4-Conjugate addition to ethenesulfonamides: serves as the aryl donor in Rh- or Pd-catalysed conjugate addition to ethenesulfonamides, giving aryl­ethanesulfonamides; the meta-chlorine is retained in the product for further derivatisation.
• Coupling with diazoesters: palladium-catalysed coupling with α-diazoesters proceeds through a metal-carbene migratory insertion to give α-aryl α,β-unsaturated esters (diarylacrylates); chloro- and bromo-substituted arylboronic acids are tolerated and retained intact under these oxidative conditions.
• Coupling with potassium cyanate: copper-catalysed coupling with potassium cyanate in an alcohol gives aryl carbamates via an aryl isocyanate intermediate.
• Chan–Lam C–N and C–O coupling: as an arylboronic acid it can transfer the 3-chlorophenyl group to amine, amide, and phenol nucleophiles under mild copper-mediated aerobic conditions.
• Oxidative ipso-hydroxylation: oxidation of the C–B bond (peroxide, persulfate, N-oxide, or photoredox) replaces boron with a hydroxyl to give 3-chlorophenol.

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.