3,4-Dichlorophenylboronic Acid | CAS 151169-75-4 | ≥98%

3,4-Dichlorophenylboronic acid ((3,4-dichlorophenyl)boronic acid) is a moderately-to-strongly electron-withdrawing trifunctional arylboronic acid building block. The combined inductive contribution of the meta- and para-chlorine substituents (Hammett σ_m(Cl) ≈ +0.37 and σ_p(Cl) ≈ +0.23) renders the aryl ring electron-deficient, consistent with a predicted lower boronic-acid pK_a relative to unsubstituted phenylboronic acid.

The 3,4-dichlorophenyl fragment is a useful motif in medicinal-chemistry scaffold design and agrochemical building-block research, and the title compound is also a documented Suzuki coupling partner for the synthesis of defined polychlorinated biphenyl (PCB) congeners used as authentic reference materials in environmental and toxicological research.

The product may contain small amounts of the cyclic anhydride 3,4-dichlorophenylboroxine; under aqueous or basic coupling conditions the two forms re-equilibrate and the impact on yield is minor.

Applications and Reactions

• Suzuki–Miyaura coupling and sequential C–Cl functionalisation: couples with aryl, heteroaryl, vinyl, and alkenyl halides or pseudohalides under Pd catalysis to install the 3,4-dichlorophenyl fragment onto biaryl, heterobiaryl, and styrenyl scaffolds. Under suitably chosen Suzuki conditions the C–B bond can be coupled while the two ring C–Cl bonds are retained in the product, providing 3,4-dichlorobiaryl and -biheteroaryl scaffolds for further elaboration. The retained C–Cl handles may be addressed in later steps under more demanding aryl-chloride activation conditions, including Buchwald–Hartwig amination, additional Suzuki coupling, or other modern Pd/phosphine-catalysed transformations (e.g., Pd/SPhos, XPhos, BrettPhos, cataCXium A, Pd(t-Bu)₃P-based systems); nucleophilic aromatic substitution should be considered only where the downstream aryl chloride is sufficiently activated by the broader scaffold (electron-withdrawing groups, electron-deficient heteroaryl context).
• Polychlorinated biphenyl (PCB) congener synthesis: the title compound is relevant to Suzuki-based routes toward defined PCB congeners and their metabolites used as authentic reference materials in environmental chemistry, toxicology, and metabolism research. Modified Suzuki coupling of chlorinated arylboronic acids with bromochlorobenzenes provides controlled access to selected polychlorinated biphenyl substitution patterns in moderate to good yields, avoiding reliance on separation from complex technical PCB mixtures. This use is documented in the peer-reviewed environmental chemistry literature.
• Medicinal-chemistry and agrochemical scaffold synthesis: the 3,4-dichlorophenyl fragment is a useful lipophilic, electron-withdrawing aryl substituent in medicinal-chemistry and agrochemical building-block research. Supplier-documented research contexts for this boronic acid include heteroaryl and biaryl scaffold construction, with specifically listed use in the synthesis of Mycobacterium tuberculosis H37Rv chorismate mutase inhibitor scaffolds. The fragment also appears in agrochemical building-block contexts, where dichloroaryl substitution is commonly used to tune lipophilicity, electronic character, and metabolic stability. As with all target-class research, the role of the 3,4-dichlorophenyl group depends on the complete molecular scaffold, substitution pattern, and selected coupling partner.
• Substituent positioning and electronic profile: the 3-Cl substituent contributes through the meta-inductive pathway with no resonance compensation (σ_m ≈ +0.37), while the 4-Cl substituent contributes net electron-withdrawing character that is partially moderated by weak π-donation from chlorine (σ_p ≈ +0.23 net). The combined substituent pattern gives an electron-deficient arylboronic acid with a predicted lower pK_a than unsubstituted phenylboronic acid, which shifts boronic-acid/boronate speciation under aqueous-basic conditions toward the boronate form. The natural-abundance ³⁵Cl/³⁷Cl isotope pattern of the dichloride substructure also provides a distinctive mass-spectrometry handle for tracking the 3,4-dichlorophenyl fragment through downstream coupling, work-up, and purification.
• Protodeboronation and condition sensitivity: class-level arylboronic-acid chemistry. Arylboronic-acid stability under aqueous-basic coupling conditions is substituent-, pH-, base-, concentration-, and temperature-dependent, so reaction conditions should be selected for the specific electrophile, base, solvent, and exposure time rather than assumed from broad electronic generalisations. Supplier documentation also lists this compound in lithiation/borylation–protodeboronation methodology involving homoallyl carbamates; that use should be treated as a methodology context unless a substrate-specific primary procedure is being cited.
• Chan–Lam coupling: class-level arylboronic-acid chemistry. The boronic acid can serve as the aryl donor in copper-mediated C–N, C–O, and C–S bond formation under aerobic conditions, transferring the 3,4-dichlorophenyl group to suitable amines, anilines, amides, phenols, alcohols, or thiols. Reaction rates and selectivity depend on the copper source, ligand, base, solvent, and nucleophile class.
• Petasis borono-Mannich reaction: class-level arylboronic-acid chemistry. Arylboronic acids can act as aryl donors in three-component reactions with an amine and an aldehyde, glyoxylic acid, or α-hydroxy aldehyde partner to give arylated amines, α-aryl glycine derivatives, or β-amino alcohol scaffolds. For 3,4-dichlorophenyl transfer, conditions should be checked against the selected carbonyl and amine partners unless a substrate-specific example is cited.
• Protected boronate ester forms: the corresponding pinacol ester (2-(3,4-dichlorophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, CAS 401797-02-2, MW 272.97) is commercially documented and provides a protected boronate form for handling and Suzuki–Miyaura coupling workflows where the free boronic acid would be inconvenient (e.g., chromatography, prolonged storage). Other slow-release boron formats, including MIDA boronates and potassium organotrifluoroborates, are class-level protection strategies for arylboronic acid handles that enable controlled-release coupling behaviour; preparation of 3,4-dichlorophenyl variants of these formats should be confirmed against substrate-specific procedures when required.

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.