2-Chloro-4-Cyanophenylboronic Acid: Properties & Applications

2-Chloro-4-cyanophenylboronic acid is a versatile bifunctional arylboronic acid building block widely employed in palladium-catalyzed cross-coupling reactions and medicinal chemistry synthesis.

Chemical Name

2-Chloro-4-cyanophenylboronic acid

SKU

C185976

Molecular Formula

C7H5BClNO2

Key Functional Groups

Boronic acid (–B(OH)2), chloro (–Cl), cyano (–CN)

Primary Application

Suzuki–Miyaura and other palladium-catalyzed cross-coupling reactions

Storage Recommendation

Store in a cool, dry place away from moisture and light

Chemical Structure and Key Properties

2-Chloro-4-cyanophenylboronic acid (SKU C185976) is an arylboronic acid bearing three distinct functional groups on a phenyl ring: a boronic acid group (–B(OH)₂) at the 1-position, a chloro substituent (–Cl) at the 2-position (ortho), and a cyano group (–CN) at the 4-position (para). The molecular formula is C₇H₅BClNO₂.

The electron-withdrawing nature of both the chloro and cyano substituents reduces the electron density of the aromatic ring, which influences the reactivity of the boronic acid moiety in transmetalation steps. The ortho-chloro group also introduces steric considerations relevant to reaction design. The cyano group can be further elaborated post-coupling—for example, via hydrolysis to carboxylic acids or reduction to amines—making this compound a highly versatile intermediate in multi-step synthesis.

As a solid boronic acid, this compound is susceptible to anhydride formation (dehydration to the corresponding boroxine) under prolonged heating or low-humidity conditions. Researchers should confirm purity by ¹¹B NMR or HPLC before use in quantitative reactions.

Applications in Cross-Coupling Chemistry

The primary application of 2-Chloro-4-cyanophenylboronic acid is as a nucleophilic coupling partner in palladium-catalyzed Suzuki–Miyaura reactions. In this context, the boronic acid undergoes transmetalation with a palladium(II) intermediate, enabling selective formation of biaryl or aryl–heteroaryl carbon–carbon bonds. The resulting biaryl products incorporating the 2-chloro-4-cyanophenyl motif are valuable intermediates in pharmaceutical and agrochemical synthesis.

The retained chloro substituent after Suzuki coupling can serve as a handle for sequential cross-coupling reactions—for instance, a second Suzuki, Buchwald–Hartwig amination, or Negishi coupling—facilitating rapid construction of complex, polysubstituted aromatic scaffolds. Similarly, the cyano group can be converted to a tetrazole (via [3+2] cycloaddition with azide) or to an amidine, both of which are pharmacophores of interest in drug discovery.

Beyond Suzuki chemistry, this boronic acid can participate in Chan–Lam coupling reactions for the construction of C–N, C–O, or C–S bonds under copper catalysis, and in rhodium-catalyzed 1,4-conjugate additions to enones, expanding its utility across multiple coupling platforms.

Role as a Medicinal Chemistry Building Block

The 2-chloro-4-cyanophenyl scaffold is frequently encountered in pharmaceutical research programs targeting a broad range of biological pathways. The chloro substituent provides lipophilicity and metabolic stability, while the cyano group is both a hydrogen-bond acceptor and a bioisostere for ester or carboxylic acid groups in certain structural contexts. Together, these features make the intact scaffold—or its coupling products—attractive candidates for structure–activity relationship (SAR) studies.

In fragment-based drug discovery (FBDD) and lead optimization, functionalized arylboronic acids such as this compound are used to rapidly diversify chemical libraries via parallel Suzuki couplings, generating arrays of biaryl analogues for biological screening. The ability to subsequently modify the cyano or chloro groups adds further combinatorial value.

Researchers engaged in kinase inhibitor, GPCR ligand, or ion-channel modulator programs may find this building block particularly useful given the prevalence of halogenated cyanobiphenyl motifs in approved drugs and clinical candidates.

Handling, Storage, and Safety Considerations

2-Chloro-4-cyanophenylboronic acid should be handled with standard laboratory precautions appropriate for organic reagents. Personal protective equipment (PPE) including nitrile gloves, safety glasses, and a laboratory coat should be worn at all times. Operations generating dust or aerosols should be conducted in a fume hood.

The compound should be stored in a tightly sealed container under cool, dry conditions, protected from moisture and direct light. Exposure to atmospheric humidity can promote boroxine formation or hydrolytic degradation over time. Long-term storage at 2–8 °C under an inert atmosphere (nitrogen or argon) is advisable to maintain reagent integrity.

The cyano group warrants attention: although aryl nitriles are generally less acutely toxic than aliphatic nitriles, appropriate precautions should still be observed. Consult the product Safety Data Sheet (SDS) for specific hazard classifications, first-aid measures, and disposal guidelines before use. Waste should be disposed of in accordance with local institutional and regulatory requirements.

Frequently asked questions

What is 2-Chloro-4-cyanophenylboronic acid primarily used for?

It is primarily used as a coupling partner in palladium-catalyzed Suzuki–Miyaura reactions to form biaryl carbon–carbon bonds. Its retained chloro and cyano groups also allow further downstream functionalization, making it a versatile building block for pharmaceutical and agrochemical synthesis.

How should I store 2-Chloro-4-cyanophenylboronic acid to maintain its purity?

Store the compound in a tightly sealed container in a cool, dry location away from moisture and light. For long-term storage, keeping the reagent at 2–8 °C under an inert atmosphere such as nitrogen or argon is recommended to prevent boroxine formation and hydrolytic degradation.

Can the cyano group of this boronic acid be further transformed after Suzuki coupling?

Yes. The cyano group in the coupled product can be hydrolyzed to a carboxylic acid, reduced to a primary amine, or converted to pharmacophoric groups such as tetrazoles or amidines. This post-coupling elaboration greatly increases the synthetic utility of this building block in medicinal chemistry programs.

What catalytic systems are typically compatible with arylboronic acids like this compound in Suzuki coupling?

Pd(PPh3)4, Pd(dppf)Cl2, and Pd(OAc)2 with phosphine ligands are commonly used palladium catalysts for Suzuki–Miyaura couplings with arylboronic acids. Bases such as K2CO3, Cs2CO3, or K3PO4 in aqueous or mixed solvent systems are typically employed. Specific conditions should be optimized for the electrophilic coupling partner used.

Is 2-Chloro-4-cyanophenylboronic acid air- and moisture-sensitive?

Arylboronic acids are generally moderately sensitive to moisture, which can promote dehydration to the boroxine anhydride or, under aqueous conditions, protodeboronation. While brief exposure to ambient conditions during weighing is typically tolerable, prolonged exposure should be avoided. Handling under inert atmosphere is advisable for critical quantitative work.

References

1. Miyaura, N.; Suzuki, A. Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds. Chem. Rev. 1995, 95, 2457–2483. doi:10.1021/cr00039a007
2. Hall, D. G. (Ed.) Boronic Acids: Preparation and Applications in Organic Synthesis, Medicine and Materials. Wiley-VCH, 2011.
3. Lennox, A. J. J.; Lloyd-Jones, G. C. Selection of boron reagents for Suzuki–Miyaura coupling. Chem. Soc. Rev. 2014, 43, 412–443. doi:10.1039/C3CS60197H

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