(2-Cyano-4-methylphenyl)boronic Acid: Handling & Use Protocol

(2-Cyano-4-methylphenyl)boronic acid is a difunctionalized arylboronic acid bearing both a nitrile group and a methyl substituent on the phenyl ring, making it a versatile electrophilic coupling partner and synthetic building block for medicinal chemistry and materials science research.

CAS Number

Needs verification — not provided in source material

Molecular Formula

C8H8BNO2

Molecular Weight

Approximately 160.97 g/mol (needs verification)

Key Functional Groups

Boronic acid (–B(OH)2), nitrile (–CN), methyl (–CH3)

Primary Application

Suzuki–Miyaura cross-coupling reactions; synthesis of biaryl and heterocyclic compounds

Storage Conditions

Store in a cool, dry place, sealed, away from moisture and light (specific temperature needs verification)

SKU

C190578

Overview and Chemical Properties

(2-Cyano-4-methylphenyl)boronic acid (SKU: C190578) is an arylboronic acid reagent featuring a ortho-cyano group and a para-methyl group relative to the boronic acid moiety on a single phenyl ring. The electron-withdrawing nitrile substituent at the 2-position modestly activates the boronic acid toward transmetalation steps in palladium-catalyzed cross-coupling reactions, while the 4-methyl group provides steric and electronic fine-tuning. The boronic acid group (–B(OH)2) is the reactive handle for Suzuki–Miyaura coupling, Chan–Lam coupling, and related transformations. The nitrile functionality offers additional synthetic handles, including conversion to amidines, tetrazoles, or heterocycles, making this compound a multifunctional building block in medicinal chemistry and materials science.

The compound is a solid at room temperature and, like most arylboronic acids, is susceptible to protodeboronation and oxidation under harsh acidic or basic aqueous conditions, and should be handled accordingly.

Safety and Storage Guidelines

Personal Protective Equipment (PPE): Always wear appropriate laboratory PPE including chemical-resistant gloves, safety goggles, and a lab coat when handling (2-Cyano-4-methylphenyl)boronic acid. Work in a well-ventilated area or fume hood, especially when weighing fine powders, to avoid inhalation of dust.

Storage: Store the compound in a tightly sealed container in a cool, dry environment, protected from moisture and direct light. Boronic acids can slowly oxidize in air and may form boroxines (anhydrides) upon prolonged exposure to heat; moisture promotes hydrolysis. Specific recommended storage temperature should be confirmed from the product certificate of analysis (CoA).

Stability: The nitrile group is generally stable under normal laboratory storage conditions but may hydrolyze slowly under strongly acidic or basic aqueous conditions at elevated temperatures. Keep away from strong oxidizing agents, strong bases, and strong acids.

Disposal: Dispose of according to local institutional and governmental regulations for chemical waste. Do not pour down the drain without appropriate treatment.

Recommended Protocol: Suzuki–Miyaura Cross-Coupling

The following is a general protocol for using (2-Cyano-4-methylphenyl)boronic acid as a coupling partner in Suzuki–Miyaura reactions. Specific conditions (catalyst loading, base, solvent, temperature, time) should be optimized for each substrate pair.

1. Materials required: (2-Cyano-4-methylphenyl)boronic acid (C190578), aryl or vinyl halide/triflate electrophile, palladium catalyst (e.g., Pd(PPh3)4 or Pd(dppf)Cl2), inorganic base (e.g., K2CO3, Cs2CO3, or Na2CO3), suitable solvent (e.g., DMF/H2O, THF/H2O, or dioxane/H2O mixture), nitrogen or argon gas supply.
2. Reaction setup: In a Schlenk flask or sealed vial, combine the aryl halide electrophile (1.0 equiv), (2-Cyano-4-methylphenyl)boronic acid (1.1–1.5 equiv), palladium catalyst (1–5 mol%), and base (2–3 equiv) in the chosen solvent system. Degas the mixture by three freeze-pump-thaw cycles or by sparging with inert gas for at least 10 minutes.
3. Reaction conditions: Stir the degassed reaction mixture under an inert atmosphere (N2 or Ar) at 80–100 °C (typical range; needs optimization per substrate) for 4–24 hours. Monitor reaction progress by TLC or LCMS.
4. Workup: Cool the reaction to room temperature. Dilute with ethyl acetate and wash with water and brine. Dry the organic layer over anhydrous Na2SO4 or MgSO4, filter, and concentrate under reduced pressure.
5. Purification: Purify the crude product by column chromatography (silica gel) or recrystallization as appropriate. Characterize the product by 1H NMR, 13C NMR, and HRMS.

Note: The ortho-cyano group may influence catalyst selection and reaction efficiency due to potential coordination to palladium. If yields are low, consider switching to a more hindered or robust palladium catalyst system.

Troubleshooting and Optimization Tips

Low conversion or yield: Ensure thorough degassing to remove dissolved oxygen, which can cause catalyst decomposition. Increase catalyst loading (up to 5–10 mol%) or switch to a more active Pd catalyst (e.g., Pd2(dba)3 with a bulky phosphine ligand). Consider raising the reaction temperature incrementally.

Homocoupling byproduct: Minimize oxygen exposure and reduce boronic acid equivalents if homocoupling is observed. Strictly anhydrous and oxygen-free conditions are critical.

Protodeboronation: If the boronic acid is consumed without coupling product formation, reduce the reaction temperature and water content. The electron-withdrawing cyano group generally reduces susceptibility to protodeboronation compared to electron-rich boronic acids, but the effect should be monitored.

Nitrile group interference: The ortho-cyano group may coordinate to palladium in certain catalyst systems, slowing catalytic turnover. Screen alternative ligands (e.g., SPhos, XPhos, or RuPhos-based Pd precatalysts) to mitigate this effect.

Solubility issues: If the boronic acid shows poor solubility, add a small amount of methanol or DMSO as co-solvent. Avoid strongly basic aqueous conditions that may hydrolyze the nitrile group.

Applications in Medicinal Chemistry and Materials Science

(2-Cyano-4-methylphenyl)boronic acid serves as a versatile building block in multiple research domains:

• Medicinal chemistry: The biaryl motif generated by Suzuki coupling of this boronic acid is prevalent in drug candidates and approved pharmaceuticals. The nitrile group can be further elaborated to amidines, primary amines (via reduction), tetrazoles (via [3+2] cycloaddition with azides), or carboxylic acids (via hydrolysis), enabling rapid generation of structurally diverse analogs for SAR studies.
• Heterocycle synthesis: The combination of the boronic acid and nitrile functionalities allows for the synthesis of fused heterocyclic scaffolds, including benzonitrile-containing biaryls, which are common pharmacophores in kinase inhibitors and other therapeutic agents.
• Materials science: Organoboron compounds and their cross-coupled products are used in the synthesis of conjugated polymers, OLED emitters, and supramolecular assemblies. The electron-withdrawing nitrile group can modulate optoelectronic properties of the resulting materials.
• Probe and sensor chemistry: Boronic acids are well-known for their reversible covalent interactions with diols, enabling the development of carbohydrate sensors and covalent capture reagents; this compound may serve as a scaffold for such applications.

Frequently asked questions

What is the primary use of (2-Cyano-4-methylphenyl)boronic acid in organic synthesis?

(2-Cyano-4-methylphenyl)boronic acid is primarily used as an aryl donor in Suzuki–Miyaura palladium-catalyzed cross-coupling reactions to construct biaryl carbon–carbon bonds. Its dual functionality — boronic acid for coupling and nitrile for further derivatization — makes it a valuable intermediate for medicinal chemistry, heterocycle synthesis, and materials research.

How should (2-Cyano-4-methylphenyl)boronic acid be stored to maintain stability?

The compound should be stored in a tightly sealed container in a cool, dry location, protected from moisture, air, and direct light. Moisture can promote boronic acid hydrolysis and boroxine formation, while oxygen exposure may lead to slow oxidation. Always consult the product Certificate of Analysis (CoA) for the manufacturer's specific storage temperature recommendation.

Can the nitrile group of this boronic acid be used for further chemical transformations?

Yes. The nitrile (–CN) group is a versatile handle for downstream synthesis. It can be reduced to a primary amine, hydrolyzed to a carboxylic acid or amide, converted to a tetrazole via [3+2] cycloaddition with azides, or transformed into an amidine. These transformations allow chemists to rapidly diversify molecular structure for drug discovery and SAR studies.

Why might the ortho-cyano group cause issues in Suzuki coupling, and how can this be addressed?

The ortho-positioned nitrile group can potentially coordinate to the palladium center, which may inhibit catalytic turnover and reduce coupling efficiency. To mitigate this, researchers should screen more hindered or electronically robust phosphine ligands (such as SPhos, XPhos, or RuPhos-based precatalysts) and ensure rigorous exclusion of oxygen to prevent catalyst deactivation.

Is (2-Cyano-4-methylphenyl)boronic acid compatible with Chan–Lam coupling conditions?

Arylboronic acids are generally compatible with Chan–Lam coupling conditions, which use copper catalysis to form C–N, C–O, or C–S bonds. (2-Cyano-4-methylphenyl)boronic acid should, in principle, be applicable to Chan–Lam coupling reactions, though specific optimization of copper source, ligand, base, and solvent would be required. Experimental validation is recommended before scale-up.

References

1. Miyaura, N.; Suzuki, A. Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds. Chemical Reviews, 1995, 95(7), 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. Chemical Society Reviews, 2014, 43(1), 412–443. doi:10.1039/c3cs60197h

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