4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one: Properties & Uses
4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one: Properties & Uses
4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one is a brominated pyrazolone heterocyclic compound widely employed as a versatile building block in medicinal chemistry, agrochemical research, and the synthesis of biologically active molecules.
- Chemical Name
- 4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one
- Core Scaffold
- Pyrazolone (five-membered N,N-containing heterocycle)
- Key Functional Groups
- C-4 bromine substituent, C-5 methyl group, C-3 ketone (lactam-like carbonyl)
- Aladdin SKU
- B1320032
- Primary Application
- Synthetic intermediate and building block in heterocyclic and medicinal chemistry
- Reactivity Highlights
- Bromine at C-4 enables cross-coupling and nucleophilic substitution; active NH supports N-alkylation and acylation
Chemical Structure and Key Properties
4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one belongs to the pyrazolone family of five-membered nitrogen-containing heterocycles. The compound features a pyrazolone ring system in which the C-3 position carries a ketone carbonyl, C-5 bears a methyl substituent, and C-4 carries a bromine atom. The ring also contains two adjacent nitrogen atoms (N-1 and N-2), with N-2 carrying a free NH group in the dihydro tautomeric form.
The presence of the bromine atom at C-4 imparts significant synthetic versatility, as it can participate in palladium-catalyzed cross-coupling reactions (e.g., Suzuki, Heck, and Sonogashira couplings) as well as nucleophilic aromatic or heteroaromatic substitution. The methyl group at C-5 modulates the electronic density of the ring, while the NH at N-2 provides a handle for N-alkylation, acylation, or sulfonylation, allowing rapid diversification of the scaffold.
Pyrazolone compounds are well documented for exhibiting tautomerism, and 4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one may exist in equilibrium between the 3-hydroxy (enol) and 3-oxo (keto) forms depending on solvent polarity and concentration.
Synthesis and Derivatization
Pyrazolone derivatives such as 4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one are classically prepared by condensation of hydrazine or substituted hydrazines with β-ketoesters or β-diketones, followed by ring closure. The introduction of the bromine at C-4 is typically achieved through electrophilic bromination of the parent 5-methyl-1,2-dihydro-3H-pyrazol-3-one using reagents such as bromine (Br₂) or N-bromosuccinimide (NBS) under controlled conditions.
Once obtained, 4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one serves as a versatile precursor for further elaboration. The C-4 bromine can be displaced by organometallic partners in cross-coupling, or substituted by amines, thiols, and other nucleophiles to introduce diverse functional groups. The NH moiety can be protected or functionalized to tune solubility, metabolic stability, and pharmacological properties of downstream compounds.
Researchers should handle brominated heterocycles with standard laboratory precautions, including the use of appropriate personal protective equipment (PPE), working in a well-ventilated fume hood, and following institutional chemical safety protocols.
Research and Medicinal Chemistry Applications
The pyrazolone scaffold is one of the most pharmacologically explored heterocyclic frameworks. Compounds bearing the 3H-pyrazol-3-one core have been reported in the literature to display a broad spectrum of biological activities, including anti-inflammatory, analgesic, antimicrobial, antifungal, antitumor, and enzyme-inhibitory properties. The incorporation of a bromine at C-4 provides a reactive handle that medicinal chemists exploit to rapidly expand structural diversity through library synthesis.
4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one is therefore of primary interest as an intermediate in the preparation of more complex pyrazolone libraries. By replacing the bromine with aryl, heteroaryl, amino, or thio groups, researchers can access a wide chemical space and perform structure–activity relationship (SAR) studies with high efficiency.
Beyond pharmaceutical research, pyrazolone derivatives find utility in dye chemistry (as coupling components in azo dye synthesis), agrochemical research (as herbicide or fungicide precursors), and as ligands in coordination chemistry for the complexation of transition metals.
Handling, Storage, and Safety Considerations
As a brominated organic compound, 4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one should be handled with appropriate care. Researchers are advised to consult the Safety Data Sheet (SDS) provided by Aladdin Scientific (SKU: B1320032) before use. General precautionary measures include avoiding inhalation of dust or vapors, preventing contact with skin and eyes, and using suitable personal protective equipment such as nitrile gloves, safety goggles, and a lab coat.
Storage is recommended in a cool, dry, well-ventilated area, away from incompatible materials such as strong oxidizers and strong bases. The compound should be kept in a tightly sealed container to prevent moisture uptake, which could promote hydrolysis or tautomeric equilibration and affect purity over time.
Waste disposal must comply with local and institutional regulations governing halogenated organic compounds. Researchers should document usage quantities and maintain appropriate chemical inventory records in accordance with institutional safety policies.
Frequently asked questions
What is 4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one used for in research?
It is primarily used as a synthetic building block and intermediate in medicinal chemistry and heterocyclic chemistry. The C-4 bromine allows cross-coupling and substitution reactions, enabling rapid construction of diverse pyrazolone-based compound libraries for biological screening and SAR studies.
Does 4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one exhibit tautomerism?
Yes. Like other pyrazolone derivatives, this compound can exist in keto (3-oxo) and enol (3-hydroxy) tautomeric forms. The predominant form in solution depends on the solvent polarity, concentration, temperature, and substituents on the ring.
What cross-coupling reactions are compatible with the C-4 bromine of this compound?
The C-4 vinyl or heteroaryl C–Br bond is potentially compatible with palladium-catalyzed Suzuki–Miyaura, Heck, Sonogashira, and Negishi cross-coupling reactions. However, reaction optimization, including base selection and protection of the NH group, may be required for best yields. Researchers should verify compatibility with their specific substrate and conditions.
How should I store 4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one to maintain purity?
Store the compound in a tightly sealed container in a cool, dry, and well-ventilated location, away from moisture, strong oxidizers, and strong bases. Always consult the Aladdin Scientific SDS (SKU: B1320032) for specific storage temperature recommendations and safety information.
Is this compound available from Aladdin Scientific and what is the product SKU?
Yes, 4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one is available from Aladdin Scientific under SKU B1320032. Contact Aladdin Scientific for current availability, pricing, and purity specifications.
References
- Elguero, J. et al. The Tautomerism of Heterocycles. Academic Press. (General reference on pyrazolone tautomerism — textbook-level background.)
- Küenburg, B. et al. Pyrazolone derivatives in medicinal chemistry: a review of biological activities. (General medicinal chemistry reference — specific article not confirmed from source material.)
- Aladdin Scientific. Product page: 4-Bromo-5-methyl-1,2-dihydro-3H-pyrazol-3-one, SKU B1320032. Aladdin Scientific catalog.
Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.
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