6-Bromo-5-Fluoroindole: Handling, Storage & Use Protocol

6-Bromo-5-fluoroindole is a halogen-substituted indole building block widely employed in medicinal chemistry and materials science as a versatile precursor for C–C and C–heteroatom bond-forming reactions.

CAS Number

1000340-39-5

Molecular Formula

C₈H₅BrFN

Molecular Weight

214.04 g/mol

Recommended Storage

Cool, dry place; sealed container; away from light

Appearance

White to off-white crystalline solid

Key Functional Sites

C-6 bromo and C-5 fluoro substituents on the indole scaffold enable selective cross-coupling and nucleophilic substitution

SKU

B124806

Safety Precautions and Risk Assessment

Before working with 6-Bromo-5-fluoroindole, review the Safety Data Sheet (SDS) supplied with the product. The compound should be treated as a potential irritant to skin, eyes, and the respiratory tract. Observe the following precautions:

• Personal Protective Equipment (PPE): Wear nitrile or latex gloves, a laboratory coat, and safety glasses or a face shield at all times during handling.
• Ventilation: All weighing and handling operations should be performed inside a well-ventilated fume hood to minimise inhalation exposure to fine particulates.
• Skin and Eye Contact: In the event of skin contact, wash the affected area immediately with soap and water for at least 15 minutes. For eye contact, rinse with copious amounts of water and seek medical attention promptly.
• Waste Disposal: Dispose of all waste in accordance with local institutional and governmental regulations for halogenated organic compounds.

No specific acute toxicity data for 6-Bromo-5-fluoroindole were identified in the source material; apply standard laboratory precautions for halogenated heterocyclic compounds until a full toxicological profile is available.

Storage and Stability Guidelines

Proper storage is critical to maintaining the purity and reactivity of 6-Bromo-5-fluoroindole over time. Follow the guidelines below:

• Temperature: Store at room temperature (15–25 °C) in a cool, dry location. Refrigeration (2–8 °C) may extend shelf life if prolonged storage is anticipated.
• Container: Keep in the original, tightly sealed container or transfer to an amber glass vial to protect from moisture and light-induced degradation.
• Atmosphere: If the compound is particularly sensitive to moisture, re-seal under an inert atmosphere (nitrogen or argon) after each use.
• Incompatibilities: Avoid contact with strong oxidising agents, strong bases, and reactive metals, which may promote undesired halogen-exchange or decomposition reactions.
• Shelf Life: Refer to the certificate of analysis (CoA) for the recommended use-by date. Verify purity by TLC or HPLC before use in critical applications if the material has been stored for an extended period.

Typical Laboratory Applications and Reaction Protocol

6-Bromo-5-fluoroindole serves as a dual-handle building block. The C-6 bromo substituent is amenable to transition-metal-catalysed cross-coupling reactions (e.g., Suzuki–Miyaura, Buchwald–Hartwig, Negishi), while the C-5 fluoro group modulates electron density, directs further electrophilic substitution, and enhances metabolic stability in drug candidates. A representative Suzuki–Miyaura coupling procedure is outlined below:

Representative Suzuki–Miyaura Coupling

1. Materials: 6-Bromo-5-fluoroindole (1.0 equiv), arylboronic acid (1.2 equiv), Pd(PPh₃)₄ or Pd(dppf)Cl₂ (2–5 mol%), K₂CO₃ or Cs₂CO₃ (2.0–3.0 equiv), degassed DMF/H₂O or dioxane/H₂O (4:1, v/v).
2. Setup: Charge a dry Schlenk flask or sealed tube with all reagents under inert atmosphere. Degas the solvent mixture by freeze-pump-thaw or sparging with nitrogen for 20 minutes.
3. Reaction: Heat the mixture at 80–100 °C for 12–18 hours with stirring, monitoring progress by TLC (UV 254 nm) or LC-MS.
4. Workup: Cool to room temperature, dilute with ethyl acetate, and wash sequentially with water and brine. Dry the organic layer (MgSO₄), filter, and concentrate in vacuo.
5. Purification: Purify by silica gel column chromatography using an appropriate hexane/ethyl acetate gradient, or by preparative HPLC if high purity is required.

Note: Specific reaction conditions (catalyst loading, base, temperature, and solvent) should be optimised for each substrate combination. The above conditions are indicative only.

Purity Verification and Analytical Characterisation

Before incorporating 6-Bromo-5-fluoroindole into a multi-step synthesis, confirm its identity and purity using one or more of the following techniques:

• Thin-Layer Chromatography (TLC): Run a small aliquot in a suitable solvent system (e.g., 9:1 hexane/EtOAc). A single spot under UV (254 nm) and/or with KMnO₄ staining provides a rapid purity assessment.
• HPLC: Reverse-phase HPLC (C18 column, acetonitrile/water gradient) should show a single dominant peak with ≥98% area purity as typically supplied.
• NMR Spectroscopy: ¹H NMR and ¹⁹F NMR in CDCl₃ or DMSO-d₆ confirm the indole NH, aromatic proton pattern, and the characteristic fluorine resonance. ¹³C NMR confirms the halogen-bearing carbons.
• Mass Spectrometry: ESI-MS or APCI-MS should show the [M+H]⁺ ion consistent with the molecular weight of 214.04 g/mol, with the characteristic bromine isotope pattern (M and M+2 in ~1:1 ratio).

Retain the certificate of analysis (CoA) supplied with each batch and archive analytical data for QC traceability.

Troubleshooting Common Issues

The following table summarises common problems encountered when working with 6-Bromo-5-fluoroindole and suggested remedies:

• Low coupling yield: Ensure complete exclusion of oxygen and moisture. Check catalyst quality and consider increasing catalyst loading (up to 5 mol%). Optimise base and solvent; switch to a more active palladium pre-catalyst if necessary.
• Multiple spots on TLC after reaction: Protodebromination or N-arylation may be competing. Lower the reaction temperature and reduce base equivalents. Consider protecting the indole nitrogen (e.g., Boc or SEM protection) before cross-coupling.
• Compound discolouration on storage: Exposure to light or moisture may cause gradual oxidation. Transfer to an amber vial, ensure tight sealing, and store under inert atmosphere.
• Poor solubility in aqueous workup: Adjust the ratio of organic solvent; ethyl acetate or dichloromethane are generally suitable extraction solvents for this class of compound.
• Unexpected N-alkylation instead of C-alkylation: In reactions with electrophiles, control reaction conditions (temperature, solvent polarity) and consider N-protection strategies to direct reactivity to the desired carbon position.

Frequently asked questions

What is the CAS number for 6-Bromo-5-fluoroindole?

The CAS number for 6-Bromo-5-fluoroindole (Aladdin SKU B124806) is 1000340-39-5. Always verify this against the certificate of analysis supplied with your batch.

How should 6-Bromo-5-fluoroindole be stored to maintain its purity?

Store 6-Bromo-5-fluoroindole in a tightly sealed container in a cool, dry, and dark location (15–25 °C). For extended storage, consider refrigeration at 2–8 °C and re-sealing under an inert gas atmosphere after each use to minimise moisture and oxidative degradation.

Which cross-coupling reactions are most suitable for 6-Bromo-5-fluoroindole?

The C-6 bromo substituent makes 6-Bromo-5-fluoroindole well-suited for palladium-catalysed Suzuki–Miyaura (with boronic acids), Buchwald–Hartwig (amination), and Negishi (organozinc) cross-coupling reactions. The C-5 fluoro group remains intact under standard cross-coupling conditions and can be exploited for subsequent nucleophilic aromatic substitution if required.

Is it necessary to protect the indole nitrogen before performing cross-coupling reactions?

N-protection is not always required but is recommended when competitive N-arylation or N-alkylation is observed as a side reaction. Common protecting groups for the indole nitrogen include Boc (tert-butoxycarbonyl) and SEM (2-(trimethylsilyl)ethoxymethyl). Evaluate the need for protection based on your specific substrate and reaction conditions.

How can I verify the purity of 6-Bromo-5-fluoroindole before use?

Purity can be confirmed by TLC (single spot under UV at 254 nm), reverse-phase HPLC (single peak, ≥98% area), ¹H and ¹⁹F NMR (consistent with the expected structure), and ESI-MS (correct molecular ion with characteristic bromine isotope pattern). Always cross-reference your results with the certificate of analysis provided by Aladdin Scientific.

References

1. Joule, J. A.; Mills, K. Heterocyclic Chemistry, 5th ed.; Wiley-Blackwell: Oxford, 2010. (General reference for indole chemistry and reactivity.)
2. Miyaura, N.; Suzuki, A. Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds. Chem. Rev. 1995, 95, 2457–2483. doi:10.1021/cr00039a007
3. Roughley, S. D.; Jordan, A. M. The Medicinal Chemist's Toolbox: An Analysis of Reactions Used in the Pursuit of Drug Candidates. J. Med. Chem. 2011, 54, 3451–3479. doi:10.1021/jm200187y

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