Cyclopentenone

2-Cyclopentenone is the organic compound with the chemical formula (CH₂)₂(CH)₂CO. 2-Cyclopentenone contains two functional groups, a ketone and an alkene. It is a colorless liquid. Its isomer, 3-cyclopentenone is less commonly encountered.

Cyclopentenone

Names
Preferred IUPAC name Cyclopent-2-en-1-one
Identifiers
CAS Number	930-30-3 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:141550
ChEMBL	ChEMBL52190 Y
ChemSpider	12999 Y
ECHA InfoCard	100.012.012
PubChem CID	13588
UNII	Q0U2IGF9CK Y
CompTox Dashboard (EPA)	DTXSID60870802
InChI InChI=1S/C5H6O/c6-5-3-1-2-4-5/h1,3H,2,4H2 Y Key: BZKFMUIJRXWWQK-UHFFFAOYSA-N Y
SMILES C1CC(=O)C=C1
Properties
Chemical formula	C5H6O
Molar mass	82.102 g·mol−1
Density	0.98 g·mL−1
Boiling point	150 °C (302 °F; 423 K)
Solubility in water	almost insoluble in water
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Harmful
Flash point	42 °C (108 °F; 315 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

The term cyclopentenone may also refer to a structural motif wherein the cyclopentenone moiety is a subunit of a larger molecule. Cyclopentenones are found in a large number of natural products, including jasmone, the aflatoxins, and several prostaglandins.^[1]

Synthesis

2-Cyclopentenones can be synthesized in a number of ways. One of the routes involves elimination of α-bromo-cyclopentanone using lithium carbonate^[2] and Claisen condensation-decarboxylation-isomerization cascades of unsaturated diesters as shown below.^[3]

Industrial synthesis of cyclopentenone

The acid-catalyzed dehydration of cyclopentanediols affords cyclopentenone.^[4]

As a functional group, the synthesis of 2-cyclopentenones is accomplished in a variety of other ways, including the Nazarov cyclization reaction from divinyl ketones, Saegusa–Ito oxidation from cyclopentanones, ring-closing metathesis from the corresponding dienes, oxidation of the corresponding cyclic allylic alcohols, and the Pauson–Khand reaction from alkenes, alkynes, and carbon monoxide.^[5]

Reactions

As an enone, 2-cyclopentenone undergoes the typical reactions of α-β unsaturated ketones, including nucleophilic conjugate addition, the Baylis–Hillman reaction, and the Michael reaction. Cyclopentenone also functions as an excellent dienophile in the Diels–Alder reaction, reacting with a wide variety of dienes. 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.^[6]

Cyclopentenone in the synthesis of coriolin

Occurrence

It has been isolated from pressure-cooked pork liver by simultaneous steam distillation and continuous solvent extraction.^[7][1]

Related compounds

• cyclopropenone
• cyclobutenone^[8]
• cyclohexenone
• cycloheptenone^[9]