Enone
Encyclopedia
An enone is an unsaturated
chemical compound
or functional group
consisting of a conjugated system
of an alkene
and a ketone
. The simplest enone is methyl vinyl ketone
(MVK) or CH2=CHCOCH3.
As an example, an enone such as a chalcone
can be synthesized in a Knoevenagel condensation
. In the Meyer–Schuster rearrangement the starting compound is a propargyl
alcohol
.
Enones undergo reactions vinylogous
to the corresponding saturated carbonyl compounds, i.e. conjugate additions. They are electrophilic also at the β-carbon, which can be attacked by nucleophile
s. Both direct addition to carbonyl and conjugate addition may occur, depending on conditions. The attack on the carbon produces a more stable compound than direct attack. An example of this is the toxicity, which follows from their ability to alkylate DNA. When the nucleophile is an hydride the reaction is called conjugate reduction.
An enone is a reactant in the Nazarov cyclization reaction
and in the Rauhut–Currier reaction (dimerization).
(R2C=C=O). An enamine
is a cousin of an enone, with the carbonyl
replaced by an amine
group. An enal is the corresponding α,β-unsaturated aldehyde
.
Saturation (chemistry)
In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...
chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
or functional group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...
consisting of a conjugated system
Conjugated system
In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in compounds with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pairs, radicals or carbenium ions may be part of the...
of an alkene
Alkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
and a ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
. The simplest enone is methyl vinyl ketone
Methyl vinyl ketone
Methyl vinyl ketone is a reactive organic compound classified as an enone. It is a colorless, flammable, highly toxic liquid with a pungent odor...
(MVK) or CH2=CHCOCH3.
As an example, an enone such as a chalcone
Chalcone
Chalcone is an aromatic ketone and an enone that forms the central core for a variety of important biological compounds, which are known collectively as chalcones or chalconoids.-Chemical synthesis:...
can be synthesized in a Knoevenagel condensation
Knoevenagel condensation
The Knoevenagel condensation reaction is an organic reaction named after Emil Knoevenagel. It is a modification of the Aldol condensation.A Knoevenagel condensation is a nucleophilic addition of an active hydrogen compound to a carbonyl group followed by a dehydration reaction in which a molecule...
. In the Meyer–Schuster rearrangement the starting compound is a propargyl
Propargyl
In organic chemistry, propargyl is an alkyl functional group of 2-propynyl with the structure HC≡C−CH2−, derived from the alkyne propyne.The term propargylic refers to a saturated position on a molecular framework next to an alkynyl group...
alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
.
Enones undergo reactions vinylogous
Vinylogous
Vinylogous is an adjective used to apply the concept of vinylogy taught in intermediate undergraduate through graduate/research organic chemistry. Vinylogy has been defined as the transmission of electronic effects through a conjugated organic bonding system...
to the corresponding saturated carbonyl compounds, i.e. conjugate additions. They are electrophilic also at the β-carbon, which can be attacked by nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
s. Both direct addition to carbonyl and conjugate addition may occur, depending on conditions. The attack on the carbon produces a more stable compound than direct attack. An example of this is the toxicity, which follows from their ability to alkylate DNA. When the nucleophile is an hydride the reaction is called conjugate reduction.
An enone is a reactant in the Nazarov cyclization reaction
Nazarov cyclization reaction
The Nazarov cyclization reaction is a chemical reaction used in organic chemistry for the synthesis of cyclopentenones. The reaction is typically divided into classical and modern variants, depending on the reagents and substrates employed...
and in the Rauhut–Currier reaction (dimerization).
Related compounds
Enone is not to be confused with KeteneKetene
A ketene is an organic compound of the form R'RC=C=O. The term is also used specifically to mean ethenone, the simplest ketene, where R' and R are hydrogen atoms.Ketenes were first studied as a class by Hermann Staudinger.-Formation:...
(R2C=C=O). An enamine
Enamine
An enamine is an unsaturated compound derived by the reaction of an aldehyde or ketone with a secondary amine followed by loss of H2O.The word "enamine" is derived from the affix en-, used as the suffix of alkene, and the root amine. This can be compared with enol, which is a functional group...
is a cousin of an enone, with the carbonyl
Carbonyl
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups....
replaced by an amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
group. An enal is the corresponding α,β-unsaturated aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
.