5-Chloro-2-ethoxyphenylboronic Acid: Properties & Lab Use
5-Chloro-2-ethoxyphenylboronic Acid: Properties & Lab Use
5-Chloro-2-ethoxyphenylboronic acid(Contains varying amounts of anhydride) is a functionalized arylboronic acid building block widely employed in palladium-catalyzed Suzuki–Miyaura cross-coupling reactions and medicinal chemistry synthesis.
- Product SKU
- C138722
- Chemical Name
- 5-Chloro-2-ethoxyphenylboronic acid (Contains varying amounts of anhydride)
- Functional Groups
- Boronic acid (–B(OH)₂), aryl chloride, and ethoxy (–OEt) substituents
- Anhydride Note
- Product contains varying amounts of the corresponding boroxine anhydride, which is reactive equivalent in coupling reactions
- Primary Application
- Suzuki–Miyaura cross-coupling, pharmaceutical intermediate synthesis
- Storage Recommendation
- Store in a cool, dry place away from moisture; seal tightly under inert atmosphere when possible
Chemical Identity and Structure
5-Chloro-2-ethoxyphenylboronic acid (SKU: C138722) is an ortho-ethoxy, para-chloro substituted arylboronic acid. The molecule features three key functional handles on the phenyl ring: a boronic acid group (–B(OH)₂) at the 1-position, an ethoxy group (–OEt) at the 2-position (ortho), and a chlorine atom at the 5-position (para relative to the ethoxy). This combination of electron-donating (ethoxy) and electron-withdrawing (chloro) substituents imparts a distinct electronic profile that influences reactivity in cross-coupling reactions.
As noted in the product specification, this compound contains varying amounts of its corresponding boroxine anhydride—a cyclic trimeric dehydration product of the boronic acid. Both the free boronic acid and its boroxine form are considered reactive equivalents in palladium-catalyzed coupling chemistry, so the presence of anhydride does not diminish synthetic utility. Researchers should account for the anhydride content when calculating molar equivalents for stoichiometric purposes.
Applications in Suzuki–Miyaura Cross-Coupling
Arylboronic acids are cornerstones of modern synthetic chemistry, and 5-Chloro-2-ethoxyphenylboronic acid is a versatile building block for constructing biaryl and heterobiaryl frameworks via the Suzuki–Miyaura reaction. In this transformation, the boronic acid couples with aryl or vinyl halides (or pseudohalides such as triflates) in the presence of a palladium catalyst and a base to form new carbon–carbon bonds with high chemoselectivity.
The aryl chloride substituent on the molecule itself may serve as an electrophilic coupling partner in sequential or orthogonal cross-coupling strategies, enabling the construction of complex polyfunctional architectures from a single starting material. The ethoxy group contributes steric and electronic modulation that can be exploited in the design of pharmaceutical candidates and agrochemical intermediates. Typical reaction conditions employ Pd(PPh₃)₄ or Pd(dppf)Cl₂ as catalyst, aqueous K₂CO₃ or Cs₂CO₃ as base, and solvents such as DMF, THF, dioxane, or ethanol/water mixtures.
Handling, Storage, and Stability
Boronic acids, including 5-Chloro-2-ethoxyphenylboronic acid, are generally air-stable solids but are susceptible to hydrolytic protodeboronation under prolonged exposure to moisture or strongly acidic/basic aqueous conditions. The equilibrium between the free boronic acid and its boroxine anhydride is moisture-dependent: humid conditions favor the free acid, while dry conditions promote anhydride formation. This interconversion is generally benign for synthetic applications.
For long-term storage, it is recommended to keep the compound sealed in its original container under dry conditions, ideally under an inert atmosphere (nitrogen or argon) at controlled room temperature or refrigerated (2–8 °C). Avoid repeated freeze-thaw cycles. When weighing or handling, standard laboratory precautions apply: use personal protective equipment (gloves, eye protection, lab coat) and work in a well-ventilated area. Consult the Safety Data Sheet (SDS) for full hazard information before use.
Role in Medicinal Chemistry and Drug Discovery
Biaryl motifs containing chloro and alkoxy substituents are recurrent pharmacophores in approved drugs and clinical candidates across therapeutic areas including oncology, cardiology, and infectious disease. 5-Chloro-2-ethoxyphenylboronic acid provides direct access to such scaffolds, making it a valuable reagent in fragment-based drug discovery (FBDD) and lead optimization campaigns.
The orthogonal reactivity of the aryl chloride and boronic acid groups enables medicinal chemists to build complexity iteratively: the boronic acid can be coupled first to establish the biaryl core, after which the chloride can be further functionalized via nucleophilic aromatic substitution, additional cross-coupling, or metal-catalyzed amination. This flexibility supports rapid analog synthesis and structure–activity relationship (SAR) exploration. Additionally, boronic acid derivatives themselves have demonstrated biological relevance as pharmacophores that form reversible covalent interactions with serine proteases, and as pharmacological tools in boron neutron capture therapy (BNCT) research contexts.
Frequently asked questions
What does 'contains varying amounts of anhydride' mean for my reaction?
The boroxine anhydride is the cyclic trimeric dehydration product of the boronic acid and is a reactive equivalent in Suzuki–Miyaura coupling reactions. Its presence does not reduce the utility of the reagent. However, you should determine or account for the anhydride content when calculating molar equivalents, as the molecular weight of the anhydride (approximately three times the boronic acid minus three water molecules) differs from that of the free acid.
Can the aryl chloride on this compound be used as a second coupling handle?
Yes. The aryl chloride substituent can serve as an electrophilic partner in subsequent palladium-catalyzed cross-coupling reactions after the boronic acid has been consumed. This orthogonal reactivity enables sequential functionalization strategies, allowing synthesis of complex polysubstituted biaryl targets from a single bifunctional building block.
How should I store 5-Chloro-2-ethoxyphenylboronic acid to maintain its quality?
Store the compound in a tightly sealed container under dry conditions, preferably under an inert atmosphere (nitrogen or argon) at room temperature or at 2–8 °C for longer-term storage. Avoid exposure to moisture, which can promote hydrolysis and protodeboronation over time. Always reseal the container promptly after use.
Which palladium catalysts are recommended for coupling reactions with this boronic acid?
Commonly used palladium catalysts for arylboronic acid Suzuki–Miyaura couplings include Pd(PPh₃)₄, Pd(OAc)₂ with phosphine ligands, and Pd(dppf)Cl₂. The optimal catalyst and base system should be determined empirically based on the specific coupling partner and reaction conditions required.
References
- Miyaura, N.; Suzuki, A. Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds. Chem. Rev. 1995, 95, 2457–2483. doi:10.1021/cr00039a007
- Hall, D. G. (Ed.) Boronic Acids: Preparation and Applications in Organic Synthesis, Medicine and Materials. Wiley-VCH, 2011.
- 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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