5-Acetyl-2-fluorobenzeneboronic acid pinacol ester: Use Protocol

5-Acetyl-2-fluorobenzeneboronic acid pinacol ester is a bench-stable, bifunctionally decorated arylboronate ester that serves as a versatile organoboron building block in palladium-catalyzed Suzuki–Miyaura cross-coupling reactions and related synthetic transformations.

CAS / SKU

A186494 (Aladdin SKU); confirm CAS with supplier documentation

Molecular Formula

C14H18BFO3 (MW ≈ 268.10 g/mol — verify with CoA)

Appearance

White to off-white crystalline solid (typical for pinacol boronate esters; confirm with CoA)

Storage Conditions

Store in a cool, dry place, sealed under inert atmosphere (N₂ or Ar), away from moisture and light

Key Functional Groups

Pinacol boronate ester (transmetalation handle), acetyl ketone (electrophilic/further functionalization), ortho-fluoro substituent (modulates electronics and enables SNAr)

Primary Application

Suzuki–Miyaura cross-coupling, SNAr reactions, pharmaceutical and agrochemical intermediate synthesis

Safety and Handling Precautions

Before using 5-Acetyl-2-fluorobenzeneboronic acid pinacol ester (SKU A186494), consult the current Safety Data Sheet (SDS) provided by Aladdin Scientific. The following general precautions apply to arylboronic acid pinacol esters:

• Personal Protective Equipment (PPE): Wear nitrile gloves, a laboratory coat, and chemical splash goggles at all times during handling.
• Ventilation: Handle in a well-ventilated fume hood to avoid inhalation of dust or vapors.
• Moisture Sensitivity: Pinacol boronate esters can hydrolyze slowly in the presence of moisture, releasing the corresponding boronic acid. Keep the container tightly sealed and use Schlenk or glovebox techniques if high purity is critical.
• Incompatibilities: Avoid contact with strong oxidizers, strong bases, and water. The acetyl group may react with strong nucleophiles or reducing agents.
• Waste Disposal: Dispose of all waste in accordance with local institutional and governmental regulations for organoboron-containing chemical waste.

Review Flag: Confirm GHS hazard classification and specific first-aid measures from the official Aladdin SDS for A186494 before use.

Storage and Stability

Proper storage of 5-Acetyl-2-fluorobenzeneboronic acid pinacol ester is essential to maintain reagent integrity over time.

• Temperature: Store at 2–8 °C or room temperature as specified on the product label and CoA. Refrigeration is generally recommended for long-term storage of boronate esters.
• Atmosphere: Store under an inert gas atmosphere (nitrogen or argon) to prevent slow oxidation and hydrolysis.
• Container: Keep in the original, tightly sealed container. Upon opening, re-seal promptly and consider transferring remaining material to a smaller vessel under inert atmosphere to minimize headspace.
• Shelf Life: Consult the expiry date on the certificate of analysis (CoA). Purity should be confirmed by TLC or HPLC before use in sensitive reactions if the reagent has been stored for extended periods.
• Purity Check: ¹H NMR in CDCl₃ or ¹¹B NMR (δ ~30 ppm for intact pinacol ester vs. ~28 ppm for free boronic acid) can confirm integrity.

Review Flag: Specific recommended storage temperature and confirmed shelf life must be verified against the Aladdin A186494 product label and CoA.

Representative Protocol: Suzuki–Miyaura Cross-Coupling

The following is a generic, textbook-level Suzuki–Miyaura coupling protocol illustrating how 5-Acetyl-2-fluorobenzeneboronic acid pinacol ester (A186494) can be employed as the boronate coupling partner. Researchers should optimize conditions for their specific substrate and target.

Materials Required

• 5-Acetyl-2-fluorobenzeneboronic acid pinacol ester (A186494), 1.0–1.5 equiv.
• Aryl halide or pseudohalide electrophilic coupling partner, 1.0 equiv.
• Palladium catalyst (e.g., Pd(PPh₃)₄ or Pd(dppf)Cl₂), 2–5 mol%
• Base (e.g., K₂CO₃, Cs₂CO₃, or K₃PO₄), 2–3 equiv.
• Solvent: DMF/H₂O (4:1 v/v), dioxane/H₂O (4:1 v/v), or THF/H₂O (3:1 v/v)
• Inert atmosphere: N₂ or Ar (balloon or Schlenk line)

General Procedure

1. Flame-dry or oven-dry the reaction vessel (round-bottom flask or pressure vial) and cool under inert gas.
2. Weigh the aryl halide electrophile, boronate ester (A186494), base, and Pd catalyst into the vessel under inert atmosphere.
3. Add degassed solvent mixture (sparge with N₂ or Ar for ≥15 min before use) via syringe.
4. Seal the vessel and stir at 80–100 °C (oil bath) for 6–16 hours. Monitor reaction progress by TLC (UV 254 nm) or LC-MS.
5. Upon completion, cool to room temperature. Dilute with ethyl acetate and wash sequentially with saturated NH₄Cl solution, water, and brine.
6. Dry the organic layer over anhydrous MgSO₄ or Na₂SO₄, filter, and concentrate under reduced pressure.
7. Purify the crude product by column chromatography (silica gel, appropriate hexanes/EtOAc gradient) or recrystallization.
8. Confirm product identity and purity by ¹H NMR, ¹³C NMR, and HRMS.

Note: The ortho-fluoro substituent in the product may be exploited in downstream SNAr reactions with amines or other nucleophiles. The acetyl group is available for further elaboration via enamine formation, aldol chemistry, or reduction.

Review Flag: Specific reaction conditions (catalyst loading, temperature, time, solvent ratio) should be validated experimentally. No specific literature example using A186494 was available in the source material; this protocol is based on standard textbook Suzuki–Miyaura methodology.

Quality Control and Purity Verification

To ensure reliable results, confirm the quality of 5-Acetyl-2-fluorobenzeneboronic acid pinacol ester (A186494) before use in critical synthetic steps:

• Certificate of Analysis (CoA): Download the batch-specific CoA from the Aladdin Scientific website using the lot number on the label. Verify purity (typically reported by HPLC or GC), melting point, and spectral data.
• ¹H NMR: Key signals expected include: aromatic protons (3H, ~δ 7.8–8.2 ppm), acetyl methyl singlet (~δ 2.6 ppm), and pinacol methyl groups (12H, ~δ 1.4 ppm). Confirm against the CoA spectrum.
• ¹¹B NMR: A single peak near δ 30 ppm is characteristic of an intact, undegraded pinacol boronate ester. Appearance of a peak near δ 28 ppm may indicate partial hydrolysis to the free boronic acid.
• HPLC Purity: ≥97% purity (by area normalization at 254 nm) is typically expected for reagent-grade material. Confirm with the specific CoA value.
• Melting Point: Confirm against the value reported in the CoA.

Review Flag: Exact NMR chemical shifts and HPLC purity specification must be confirmed against the Aladdin A186494 CoA; values above are estimates based on structurally analogous arylboronate esters.

Downstream Synthetic Applications

The unique combination of functional groups in 5-Acetyl-2-fluorobenzeneboronic acid pinacol ester (A186494) makes it a versatile intermediate for multi-step synthesis:

• Suzuki–Miyaura Cross-Coupling: The boronate ester undergoes palladium-catalyzed transmetalation with aryl, heteroaryl, vinyl, or benzyl halides and triflates to construct biaryl or styryl scaffolds bearing the electron-withdrawing acetyl and ortho-fluoro groups.
• SNAr Reactions: After Suzuki coupling, or independently, the ortho-fluoro group (activated by the adjacent electron-withdrawing acetyl group) can participate in nucleophilic aromatic substitution (SNAr) with primary or secondary amines, alkoxides, or thiolates under mild to moderate conditions, providing access to amine-, ether-, or thioether-substituted arenes.
• Acetyl Group Manipulation: The acetyl ketone can be: (a) reduced to the corresponding benzylic alcohol using NaBH₄ or LiAlH₄; (b) converted to an enamine or oxime for further transformations; (c) used in Baeyer–Villiger oxidation to access the phenyl ester or phenol; or (d) employed in aldol-type condensations.
• Pharmaceutical and Agrochemical Intermediates: Fluorinated biaryl acetyl motifs are privileged scaffolds in medicinal chemistry for kinase inhibitor, GPCR ligand, and agrochemical active ingredient development.

Review Flag: All downstream applications listed here are based on well-established textbook-level organic chemistry for analogous substrates. No specific literature references for A186494 were provided in the source material.

Frequently asked questions

How should I handle 5-Acetyl-2-fluorobenzeneboronic acid pinacol ester (A186494) to prevent hydrolysis?

Store and handle A186494 under an inert atmosphere (N₂ or Ar) in a tightly sealed container away from moisture. When weighing or transferring, work quickly or use Schlenk or glovebox techniques. Use freshly dried and degassed solvents in reactions. If extended storage is required, refrigeration under inert gas is recommended.

Can the boronate ester be used directly in Suzuki coupling without prior hydrolysis to the boronic acid?

Yes. Arylboronic acid pinacol esters are competent coupling partners in Suzuki–Miyaura reactions under standard conditions (Pd catalyst, base, aqueous co-solvent). The base and water present in the reaction mixture facilitate in situ hydrolysis or direct transmetalation. In some cases, activation with fluoride or addition of excess base improves reactivity of hindered or electron-poor boronate esters.

What is the significance of the ortho-fluoro substituent in this compound?

The ortho-fluoro group serves multiple roles: it electronically modulates the arene ring, making it more electron-deficient, which can influence coupling reactivity and regioselectivity. It also enables downstream SNAr reactions with nucleophiles such as amines or alkoxides, providing an additional handle for diversification. In pharmaceutical contexts, fluorine substituents are valued for improving metabolic stability and membrane permeability of drug candidates.

How do I confirm the purity and identity of A186494 upon receipt?

Download the batch CoA from the Aladdin Scientific website using the lot number on the vial. Check the reported purity by HPLC or GC, and compare spectral data (¹H NMR, melting point) against CoA values. A ¹¹B NMR spectrum showing a single peak near δ 30 ppm confirms an intact pinacol boronate ester and absence of significant hydrolysis.

Is A186494 suitable for use in reactions requiring anhydrous conditions?

Pinacol boronate esters are generally more hydrolytically stable than the corresponding free boronic acids and can tolerate mildly aqueous conditions such as those used in Suzuki coupling. However, for reactions that are strictly anhydrous (e.g., organolithium or Grignard additions to the acetyl group), ensure the substrate is dry prior to use by storing over molecular sieves or drying briefly under high vacuum.

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, 2nd ed.; Wiley-VCH: Weinheim, 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
4. Aladdin Scientific. Product Page and Certificate of Analysis for 5-Acetyl-2-fluorobenzeneboronic acid pinacol ester, SKU A186494. https://www.aladdin-e.com

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.