2-Amino-5-Chloro-3-Iodopyridine: Handling & Synthesis Protocol
2-Amino-5-Chloro-3-Iodopyridine: Handling & Synthesis Protocol
2-Amino-5-chloro-3-iodopyridine is a versatile halogenated pyridine building block widely employed in palladium- and copper-catalyzed cross-coupling reactions for the construction of complex heterocyclic frameworks in medicinal and synthetic chemistry.
- CAS Number
- 796851-05-3
- Molecular Formula
- C₅H₄ClIN₂
- Molecular Weight
- 254.46 g/mol
- Appearance
- Off-white to pale yellow solid
- Storage Condition
- Store at 2–8 °C, away from light and moisture
- SKU
- C132073
- Primary Application
- Cross-coupling reactions (Suzuki, Negishi, Buchwald-Hartwig) and directed metalation
Safety and Pre-Handling Precautions
Before working with 2-Amino-5-chloro-3-iodopyridine (C132073), review the Safety Data Sheet (SDS) supplied by Aladdin Scientific. The compound contains both iodo and chloro substituents and should be treated as a potential irritant.
- Personal Protective Equipment (PPE): Wear nitrile gloves, a laboratory coat, and safety goggles at all times during handling.
- Ventilation: Handle in a well-ventilated fume hood to minimize inhalation exposure to fine particulates.
- Moisture Sensitivity: Although not strongly hygroscopic, prolonged exposure to atmospheric moisture may promote degradation; keep the container tightly sealed when not in use.
- Light Sensitivity: Iodinated aromatics can be light-sensitive; store the compound in amber vials or foil-wrapped containers.
- First Aid: In case of skin or eye contact, flush immediately with copious water for at least 15 minutes and seek medical attention.
Solubility and Solution Preparation
2-Amino-5-chloro-3-iodopyridine is soluble in common organic solvents. Use the following guidance to prepare stock and working solutions:
- Recommended Solvents: Dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), dichloromethane (DCM), tetrahydrofuran (THF), and ethyl acetate. Aqueous solubility is limited; avoid water as primary solvent.
- Stock Solution Preparation: Weigh the required amount of C132073 into a tared glass vial. Add anhydrous solvent (e.g., DMSO) dropwise with gentle vortexing until fully dissolved. Prepare 0.1–0.5 M stock solutions for synthetic use.
- Filtration: If any particulates remain, filter through a 0.2 µm PTFE syringe filter before use in sensitive reactions.
- Storage of Solutions: Prepared solutions should be stored at –20 °C under inert atmosphere (nitrogen or argon) and used within 4 weeks. Avoid repeated freeze-thaw cycles.
Note: Specific solubility values (mg/mL) for this compound are not confirmed in the current source material; verify against the product specification sheet (C132073) before use.
Representative Protocol: Suzuki-Miyaura Cross-Coupling
The C–I bond of 2-Amino-5-chloro-3-iodopyridine undergoes selective oxidative addition to palladium(0) in preference to the C–Cl bond, enabling chemoselective Suzuki-Miyaura coupling at the 3-position while retaining the 5-chloro handle for subsequent functionalization.
General Procedure (0.25 mmol scale)
- Reagents: 2-Amino-5-chloro-3-iodopyridine (1.0 equiv, 63.6 mg, 0.25 mmol), arylboronic acid (1.2 equiv), Pd(PPh₃)₄ (5 mol%), K₂CO₃ (2.0 equiv), 1,4-dioxane/H₂O (4:1, 2.5 mL).
- Setup: Charge a flame-dried Schlenk flask or sealed vial with the substrate, boronic acid, catalyst, and base under nitrogen or argon atmosphere.
- Solvent Addition: Add degassed solvent mixture via syringe. Seal the vessel.
- Reaction: Heat at 80–90 °C with stirring for 12–16 hours. Monitor conversion by TLC (e.g., hexane/EtOAc 3:1, UV 254 nm).
- Workup: Cool to room temperature. Dilute with EtOAc (20 mL) and wash with water (2 × 10 mL) and brine (10 mL). Dry over anhydrous Na₂SO₄, filter, and concentrate under reduced pressure.
- Purification: Purify by silica gel column chromatography (gradient: hexane to hexane/EtOAc).
Caution: Specific yields and exact conditions for this substrate have not been confirmed by Aladdin Scientific source data; these conditions represent general guidance for iodopyridine Suzuki coupling. Optimize conditions empirically before scale-up.
Alternative Transformations and Applications
Beyond Suzuki coupling, 2-Amino-5-chloro-3-iodopyridine serves as a multifunctional platform for diverse synthetic transformations:
- Buchwald-Hartwig Amination: The C–I bond can participate in palladium-catalyzed amination reactions to install secondary amine functionalities, leveraging the reactivity differential between C–I and C–Cl bonds.
- Negishi Coupling: Organozinc reagents can be coupled selectively at the 3-iodo position under standard Pd(0) catalysis.
- Sonogashira Coupling: Terminal alkynes react at the C–I site under Pd/Cu co-catalysis (e.g., Pd(PPh₃)₂Cl₂, CuI, Et₃N) to afford 3-alkynylpyridine derivatives.
- Directed Ortho-Metalation / Regioselective Functionalization: The 2-amino group acts as a directing group for further lithiation or metalation strategies, enabling access to tri- and tetra-substituted pyridine scaffolds.
- Sequential Functionalization: Because the C–I bond is more reactive than C–Cl in oxidative addition, sequential cross-coupling can install two different substituents at positions 3 and 5, providing access to structurally diverse biaryl or heteroaryl-pyridine scaffolds relevant to drug discovery.
Quality Control and Troubleshooting
To ensure reliable results when using C132073, follow these quality control and troubleshooting recommendations:
| Issue | Likely Cause | Recommended Action |
|---|---|---|
| Low coupling yield | Catalyst deactivation or insufficient degassing | Thoroughly degas all solvents with freeze-pump-thaw or sparging; use fresh Pd catalyst |
| Undesired C–Cl coupling | Excess catalyst or high temperature | Reduce catalyst loading and lower reaction temperature; use milder Pd precatalyst |
| Compound discoloration | Degradation from light or moisture exposure | Check storage conditions; reconfirm purity by HPLC or ¹H NMR before use |
| Poor solubility in reaction mixture | Incompatible solvent or low temperature | Switch to DMF or DMSO co-solvent; warm gently to 40 °C before adding to reaction |
| Protodeiodination side product | Trace protic impurities or high temperature | Use anhydrous solvents and maintain temperature ≤90 °C |
Always confirm the identity and purity of C132073 by ¹H NMR, ¹³C NMR, or HPLC against the certificate of analysis (CoA) provided by Aladdin Scientific before initiating critical experiments.
Frequently asked questions
What makes the C–I bond more reactive than the C–Cl bond in 2-Amino-5-chloro-3-iodopyridine?
The C–I bond is weaker and more polarizable than the C–Cl bond, resulting in a lower barrier to oxidative addition into palladium(0) complexes. This reactivity difference allows chemists to selectively functionalize the 3-iodo position while leaving the 5-chloro group intact for subsequent synthetic steps.
How should I store 2-Amino-5-chloro-3-iodopyridine (C132073) to maintain its integrity?
Store C132073 at 2–8 °C in a tightly sealed container, protected from light and atmospheric moisture. For long-term storage, an inert atmosphere (nitrogen or argon) is recommended. Confirm purity by NMR or HPLC after extended storage periods before use in sensitive applications.
Can 2-Amino-5-chloro-3-iodopyridine be used in aqueous reaction systems?
This compound has limited aqueous solubility. For reactions requiring aqueous co-solvent systems (such as Suzuki coupling in dioxane/water mixtures), dissolve the compound first in the organic component before adding the aqueous phase. Avoid purely aqueous conditions, as incomplete dissolution may reduce reaction efficiency.
Which palladium catalyst is recommended for Suzuki coupling with C132073?
Pd(PPh₃)₄ is a common and effective choice for Suzuki-Miyaura coupling of iodopyridines. Alternatives such as Pd(dppf)Cl₂ or Pd₂(dba)₃ with a suitable phosphine ligand may improve yields for sterically hindered or electron-deficient substrates. The optimal catalyst should be determined empirically for each specific coupling partner.
Is 2-Amino-5-chloro-3-iodopyridine suitable for drug discovery applications?
Yes, this compound is a valuable building block in medicinal chemistry. Its aminopyridine core is a privileged scaffold in drug discovery, and the combination of halogen handles at positions 3 and 5 enables sequential diversification to generate structurally complex analogue libraries for structure-activity relationship (SAR) studies.
References
- Miyaura, N.; Suzuki, A. Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds. Chem. Rev. 1995, 95, 2457–2483. doi:10.1021/cr00039a007
- Hartwig, J. F. Transition Metal Catalyzed Synthesis of Arylamines and Aryl Ethers from Aryl Halides and Triflates: Scope and Mechanism. Angew. Chem. Int. Ed. 1998, 37, 2046–2067. doi:10.1002/(SICI)1521-3773(19980817)37:15<2046::AID-ANIE2046>3.0.CO;2-L
- Sonogashira, K.; Tohda, Y.; Hagihara, N. A Convenient Synthesis of Acetylenes: Catalytic Substitutions of Acetylenic Hydrogen with Bromoalkenes, Iodoarenes and Bromopyridines. Tetrahedron Lett. 1975, 16, 4467–4470. doi:10.1016/S0040-4039(00)91094-3
- Aladdin Scientific. Product Specification Sheet: 2-Amino-5-chloro-3-iodopyridine, SKU C132073. Aladdin Scientific, Shanghai.
Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.
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