2-Methyl-2-cyclohexen-1-one: Handling & Application Protocol

2-Methyl-2-cyclohexen-1-one is a versatile cyclic α,β-unsaturated ketone (enone) widely employed as a Michael acceptor and synthetic building block in the preparation of terpenoids, pharmaceuticals, and other complex carbocyclic targets.

CAS Number

1121-18-2

Molecular Formula

C₇H₁₀O

Molecular Weight

110.15 g/mol

Appearance

Colorless to pale yellow liquid

Aladdin SKU

M463131

Key Functional Group

α,β-Unsaturated ketone (enone); acts as Michael acceptor at the β-carbon

Storage Condition

Store at room temperature, away from light, heat, and moisture; keep container tightly sealed

Reagent Overview and Properties

2-Methyl-2-cyclohexen-1-one (Aladdin SKU: M463131; CAS 1121-18-2) is a six-membered cyclic enone bearing a methyl substituent at the α-position of the carbonyl. Its conjugated system makes the β-carbon electrophilic, rendering the compound an excellent Michael acceptor in 1,4-conjugate addition reactions.

The compound is a colorless to pale yellow liquid with a molecular weight of 110.15 g/mol and molecular formula C₇H₁₀O. It is miscible with common organic solvents including dichloromethane, tetrahydrofuran, ethyl acetate, and acetonitrile, but has limited water miscibility. Its α,β-unsaturated carbonyl framework is a privileged motif found in numerous natural products, including pulegone-related terpenoids.

Safety, Handling, and Storage

Personal Protective Equipment (PPE): Handle 2-Methyl-2-cyclohexen-1-one in a well-ventilated fume hood. Wear appropriate chemical-resistant gloves (e.g., nitrile), safety goggles, and a laboratory coat at all times. Avoid inhalation of vapors and contact with skin or eyes.

Storage: Store at room temperature in a tightly sealed amber or opaque container, away from heat sources, direct light, and moisture. Keep away from strong oxidizers and bases. Follow your institution's chemical inventory and waste-disposal regulations for ketone-containing materials.

Disposal: Dispose of waste material in accordance with local, regional, and national regulations for organic solvent waste. Do not pour down the drain. Consult your institutional safety office for guidance.

Note: Always consult the current Safety Data Sheet (SDS) before use.

Standard Protocol: Preparation and Use in 1,4-Conjugate Addition

The following protocol outlines a general procedure for using 2-Methyl-2-cyclohexen-1-one (M463131) as an acceptor substrate in organocatalytic or Lewis acid-mediated 1,4-conjugate addition reactions. Specific conditions (catalyst, nucleophile, solvent, temperature) should be optimized according to the target transformation and literature precedent.

1. Reagent preparation: Allow the reagent vial to equilibrate to room temperature before opening. Inspect the liquid for clarity and color; discard if turbidity or heavy discoloration is observed.
2. Reaction setup: In a dry, inert-atmosphere flask (N₂ or Ar), charge the appropriate solvent (e.g., CH₂Cl₂ or THF) and catalyst. Add 2-Methyl-2-cyclohexen-1-one (1.0 equiv) via microsyringe or disposable pipette. Add the nucleophilic partner (e.g., malonate, amine, or organocuprate) as specified by your protocol.
3. Reaction monitoring: Monitor reaction progress by thin-layer chromatography (TLC) or analytical HPLC at appropriate time intervals. Use UV-active silica TLC plates; the enone absorbs UV at ~230 nm.
4. Workup: Upon reaction completion, quench as appropriate (e.g., saturated NH₄Cl aqueous solution for organometallic reactions). Extract with an organic solvent, dry over anhydrous MgSO₄ or Na₂SO₄, filter, and concentrate under reduced pressure.
5. Purification: Purify the product by flash column chromatography on silica gel using a suitable eluent system. Confirm product identity by ¹H NMR, ¹³C NMR, and MS.

Tip: Because the enone is volatile and reactive, minimize exposure to air and use freshly transferred aliquots for best reproducibility.

Analytical Characterization

Confirm the identity and purity of 2-Methyl-2-cyclohexen-1-one using the following analytical methods:

• ¹H NMR (400 MHz, CDCl₃): Characteristic signals include the vinyl proton at the β-carbon (~δ 5.9–6.0 ppm), the α-methyl singlet (~δ 1.9 ppm), and methylene protons of the cyclohexenone ring (~δ 2.0–2.5 ppm). Exact chemical shifts should be verified against a primary reference.
• IR Spectroscopy: A strong C=O stretch is expected in the region ~1670–1690 cm⁻¹ (conjugated enone carbonyl), and C=C stretch ~1620 cm⁻¹.
• GC Purity: Assess purity by gas chromatography (GC-FID) with a non-polar capillary column. Target purity ≥97% for synthetic applications.
• Mass Spectrometry: Expected molecular ion [M]⁺ at m/z = 110.07 (EI-MS).

Note: Exact NMR assignments should be confirmed against authenticated reference spectra or literature values. The above values are indicative and subject to review.

Troubleshooting and Quality Control

Common issues and recommended solutions:

• Low conversion in conjugate addition: Check catalyst loading and ensure anhydrous conditions. Moisture can deactivate Lewis acid catalysts and degrade reaction efficiency. Pre-dry all solvents and glassware.
• Product decomposition: Avoid prolonged exposure to acidic or strongly basic conditions during workup, as the enone ring can undergo side reactions. Maintain mild workup conditions.
• Reagent discoloration: If the stored reagent has turned dark or developed a precipitate, assess purity by GC before use. Redistillation under reduced pressure may be considered to recover pure material (consult your safety officer first).
• Poor TLC resolution: Optimize eluent polarity. Typical starting points for enone-containing mixtures include hexane/EtOAc (9:1 to 4:1 v/v).

Quality control checklist before use: (1) Verify CAS number and lot number match the SDS. (2) Inspect reagent appearance. (3) Confirm GC purity ≥97%. (4) Review SDS for any updated hazard information.

Frequently asked questions

What is 2-Methyl-2-cyclohexen-1-one primarily used for in organic synthesis?

2-Methyl-2-cyclohexen-1-one is widely used as a Michael acceptor in 1,4-conjugate addition reactions, as a starting material for terpenoid and natural product synthesis, and as a versatile enone building block for constructing carbocyclic frameworks. Its α,β-unsaturated carbonyl system enables a broad range of enantioselective organocatalytic transformations.

How should 2-Methyl-2-cyclohexen-1-one (M463131) be stored to maintain reagent quality?

Store M463131 at room temperature in a tightly sealed, light-protected container away from heat, moisture, and strong oxidizing agents. Ensure the container is properly labeled and check for discoloration or turbidity before each use. Consult the current SDS for detailed storage and hazard information.

Which nucleophiles are commonly used with 2-Methyl-2-cyclohexen-1-one in Michael addition reactions?

Common nucleophiles include stabilized carbanions from malonates and β-ketoesters, secondary amines, organocuprates (R₂CuLi), and enolates generated from ketones or aldehydes. The choice of nucleophile depends on the desired product and reaction conditions (organocatalytic, transition-metal-catalyzed, or stoichiometric).

How can I confirm the purity of 2-Methyl-2-cyclohexen-1-one before use?

Purity can be assessed by GC-FID using a non-polar capillary column; a purity of ≥97% is recommended for most synthetic applications. Additionally, ¹H NMR in CDCl₃ and comparison with reference spectral data provide reliable structural confirmation. Check the certificate of analysis (CoA) provided with the product lot.

References

1. Sigma-Aldrich (Merck). 2-Methyl-2-cyclohexen-1-one, Product No. 771368. Product information and SDS available on the Sigma-Aldrich website.
2. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. 4th ed. Wiley-Interscience, 1992. Chapter on Michael Addition reactions.
3. Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry. 2nd ed. Oxford University Press, 2012. Discussion of conjugate addition to enones.

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