Cyclohexenone is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

which is a versatile intermediate used in the

synthesis Synthesis or synthesize may refer to: Science Chemistry and biochemistry *Chemical synthesis, the execution of chemical reactions to form a more complex molecule from chemical precursors **Organic synthesis, the chemical synthesis of organi ...

of a variety of chemical products such as pharmaceuticals and fragrances. It is colorless liquid, but commercial samples are often yellow. Industrially, cyclohexenone is prepared from

phenol Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group () ...

Birch reduction The Birch reduction or Metal-Ammonia reduction is an organic reaction that is used to convert arenes to Cyclohexa-1,4-diene, 1,4-cyclohexadienes. The reaction is named after the Australian chemist Arthur Birch (organic chemist), Arthur Birch and i ...

. Cyclohexenone is a

ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...

, or more precisely an enone. Common reactions include nucleophilic conjugate addition with organocopper reagents,

Michael reaction In organic chemistry, the Michael reaction or Michael 1,4 addition is a reaction between a Michael donor (an enolate or other nucleophile) and a Michael acceptor (usually an α,β-unsaturated carbonyl) to produce a Michael adduct by creating a c ...

s and

Robinson annulation The Robinson annulation is a chemical reaction used in organic chemistry for ring formation. It was discovered by Robert Robinson (organic chemist), Robert Robinson in 1935 as a method to create a six membered ring by forming three new carbon–c ...

Synthesis

Several routes exist for the production of cyclohexenone. For the laboratory scale, it can be produced from

resorcinol Resorcinol (or resorcin) is a phenolic compound. It is an organic compound with the formula C6H4(OH)2. It is one of three isomeric benzenediols, the 1,3-isomer (or ''meta- (chemistry), meta''-isomer). Resorcinol crystallizes from benzene as co ...

via 1,3-cyclohexanedione. : Cyclohexenon Synthese

Cyclohexenone is obtained by

anisole Anisole, or methoxybenzene, is an organic compound with the formula . It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances. The compound is mainly ...

followed by acid hydrolysis. : Birch Anisol

It can be obtained from cyclohexanone by α-bromination followed by treatment with base. Hydrolysis of 3-chloro cyclohexene followed by oxidation of the cyclohexenol is yet another route. Cyclohexenone is produced industrially by catalytic oxidation of cyclohexene, for example with

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

and

vanadium Vanadium is a chemical element; it has Symbol (chemistry), symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an ...

catalysts. Several patents describe diverse oxidizing agents and catalysts.

Reactions

Cyclohexenone is a widely used building block in organic synthesis chemistry, as it offers many different ways to extend molecular frameworks. As an enone, cyclohexenone is easily adapted to

Michael addition In organic chemistry, the Michael reaction or Michael 1,4 addition is a reaction between a Michael donor (an enolate or other nucleophile) and a Michael acceptor (usually an α,β-unsaturated carbonyl) to produce a Michael adduct by creating a c ...

with nucleophiles (such as

enolate In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl () compounds. Rarely isolated, they are widely used as reagents in the Organic synthesis, synthesis of organic compounds. Bonding and structure Enolate ...

s or silyl enol ethers) or, it could be employed by a Diels-Alder reaction with electron-rich

diene In organic chemistry, a diene ( ); also diolefin, ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alk''ene'' units, with the standard prefix ''di'' of systematic nome ...

s. Furthermore, this compound reacts with

organocopper compound Organocopper chemistry is the study of the physical properties, reactions, and synthesis of organocopper compounds, which are organometallic compounds containing a carbon to copper chemical bond. They are reagents in organic chemistry. The f ...

s from 1,4-addition (Michael addition), or with Grignard reagents 1,2-addition, i.e., with attack of the nucleophile at the carbonyl carbon atom. Cyclohexenone is also used in multi-step synthesis in the construction of polycyclic natural products. It is prochiral. With strong bases, the positions 4 and 6 (the two CH₂-groups of the carbonyl group and the C-C double bond adjacent) are deprotonated. Cyclohexenone is an ''in-vitro'' catalyst for a relatively mild

decarboxylation Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is ...

of alpha amino acids.Researchers in Japan were attempting to use t-butyl peroxide as a catalyst for decarboxylation using a solvent choice of

cyclohexanol Cyclohexanol is the organic compound with the formula HOCH(CH2)5. The molecule is related to cyclohexane by replacement of one hydrogen atom by a hydroxyl group. This compound exists as a deliquescent colorless solid with a camphor-like odor, whi ...

. Curiously they found that when they used lower-purity (e.g. technical grade, 98%) cyclohexanol, the reaction proceeded as much as 4 times faster compared to when they used relatively pure cyclohexanol (>99.3%). They found that cyclohexanol contained cyclohexenone as a natural impurity, which was three times more abundant in the technical grade cyclohexenone compared to the more purified cyclohexanol (~0.3% versus ~0.1%). Further research showed that 1% cyclohexenone in cyclohexanol will decarboxylate most alpha-amino acids, including non-standard ones, with a yield of 80-95% in a matter of several hours. The exceptions are certain amino acids like

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an Amine, α-amino group (which is in the protonated –NH3+ form under Physiological condition, biological conditions), a carboxylic ...

, which was reported to take over 26 hours, and poly-amino acids, which fail to decarboxylate using 2-cyclohexenone and another route must be found instead.

Related compounds

* cyclopropenone *cyclobutenone *

cyclopentenone 2-Cyclopentenone is the organic compound with the chemical formula . 2-Cyclopentenone contains two functional groups, a ketone and an alkene. It is a colorless liquid. Its isomer, 3-cyclopentenone is less commonly encountered. The term cyclopent ...

*cycloheptenone

References

{{Reflist Enones Reagents for organic chemistry Cyclohexenes