2-Cyclopentenone is a
ketone with
chemical formula
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...
and
CAS number
A CAS Registry Number (also referred to as CAS RN or informally CAS Number) is a unique identification number assigned by the Chemical Abstracts Service (CAS), US to every chemical substance described in the open scientific literature. It inclu ...
930-30-3. It is structurally similar to
cyclopentanone
Cyclopentanone is the organic compound with the formula (CH2)4CO. This cyclic ketone is a colorless volatile liquid.
Preparation
Upon treatment with barium hydroxide at elevated temperatures, adipic acid undergoes ketonization to give cyclopent ...
, with the additional feature of
α-β unsaturation in the ring system. 2-Cyclopentenone contains two functional groups, a ketone and an alkene. It is a colorless liquid.
The term cyclopentenone may also refer to a
structural motif wherein the cyclopentenone
moiety
Moiety may refer to:
Chemistry
* Moiety (chemistry), a part or functional group of a molecule
** Moiety conservation, conservation of a subgroup in a chemical species
Anthropology
* Moiety (kinship), either of two groups into which a society is ...
is a subunit of a larger molecule. Cyclopentenones are found in a large number of
natural products, including
jasmone, the
aflatoxin
Aflatoxins are various poisonous carcinogens and mutagens that are produced by certain molds, particularly ''Aspergillus'' species. The fungi grow in soil, decaying vegetation and various staple foodstuffs and commodities such as hay, sweetcorn ...
s, and several
prostaglandins.
Synthesis
2-Cyclopentenones can be synthesized in a number of ways. One of the routes involves elimination of α-
bromo-
cyclopentanone
Cyclopentanone is the organic compound with the formula (CH2)4CO. This cyclic ketone is a colorless volatile liquid.
Preparation
Upon treatment with barium hydroxide at elevated temperatures, adipic acid undergoes ketonization to give cyclopent ...
using
lithium carbonate and
Claisen condensation
The Claisen condensation is a carbon–carbon bond forming reaction that occurs between two esters or one ester and another carbonyl compound in the presence of a strong base, resulting in a β-keto ester or a β-diketone. It is named after Ra ...
-
decarboxylation-
isomerization
In chemistry, isomerization or isomerisation is the process in which a molecule, polyatomic ion or molecular fragment is transformed into an isomer with a different chemical structure. Enolization is an example of isomerization, as is tautomeriz ...
cascades of unsaturated
diester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides a ...
s as shown below.
The acid-catalyzed dehydration of cyclopentanediols affords cyclopentenone.
As a functional group, the synthesis of 2-cyclopentenones is accomplished in a variety of other ways, including the
Nazarov cyclization reaction
The Nazarov cyclization reaction (often referred to as simply the Nazarov cyclization) is a chemical reaction used in organic chemistry for the synthesis of cyclopentenones. The reaction is typically divided into ''classical'' and ''modern'' var ...
from divinyl ketones,
Saegusa–Ito oxidation from
cyclopentanone
Cyclopentanone is the organic compound with the formula (CH2)4CO. This cyclic ketone is a colorless volatile liquid.
Preparation
Upon treatment with barium hydroxide at elevated temperatures, adipic acid undergoes ketonization to give cyclopent ...
s,
ring-closing metathesis
Ring-closing metathesis (RCM) is a widely used variation of olefin metathesis in organic chemistry for the synthesis of various unsaturated rings via the intramolecular metathesis of two terminal alkenes, which forms the cycloalkene as the ''E-' ...
from the corresponding
diene
In organic chemistry a diene ( ) (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 nomenclature. ...
s,
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
of the corresponding cyclic
allylic alcohol
Allyl alcohol (IUPAC name: prop-2-en-1-ol) is an organic compound with the structural formula . Like many alcohols, it is a water-soluble, colourless liquid. It is more toxic than typical small alcohols. Allyl alcohol is used as a raw material ...
s, and the
Pauson–Khand reaction
The Pauson–Khand reaction (or PKR or PK-type reaction) is a chemical reaction described as a 2+2+1.html" ;"title="/nowiki>2+2+1">/nowiki>2+2+1/nowiki> cycloaddition between an alkyne, an alkene and carbon monoxide to form a α,β- cyclopentenon ...
from
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s,
alkynes, and
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
.
Reactions
As an
enone, 2-cyclopentenone undergoes the typical reactions of α-β unsaturated ketones, including
nucleophilic conjugate addition, the
Baylis–Hillman reaction
The Baylis–Hillman reaction is a carbon-carbon bond forming reaction between the α-position of an activated alkene and a carbon electrophile such as an aldehyde. Employing a nucleophilic catalyst, such as a tertiary amine and phosphine, this rea ...
, and the
Michael reaction
In organic chemistry, the Michael reaction or Michael 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 carbon ...
. Cyclopentenone also functions as an excellent
dienophile in the
Diels–Alder reaction, reacting with a wide variety of
diene
In organic chemistry a diene ( ) (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 nomenclature. ...
s. In one example, a
Danishefsky-type diene is reacted with a cyclopentenone to yield a fused tricyclic system en route to the synthesis of coriolin.
Occurrence
It has been isolated from pressure-cooked pork
liver
The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
by simultaneous steam
distillation
Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heat ...
and continuous
solvent extraction
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
.
References
{{reflist
Enones
Cyclopentenes