Cyclopentenone

Cyclopentenone
IUPAC name 2-Cyclopenten-1-one
Identifiers
CAS number	930-30-3 Y
PubChem	13588
ChemSpider	12999 Y
ChEMBL	CHEMBL52190 Y
Jmol-3D images	Image 1
SMILES C1CC(=O)C=C1
InChI InChI=1S/C5H6O/c6-5-3-1-2-4-5/h1,3H,2,4H2 Y Key: BZKFMUIJRXWWQK-UHFFFAOYSA-N Y
Properties
Molecular formula	C5H6O
Molar mass	82.04 g·mol−1
Density	0.98 g·mL−1
Boiling point	150 °C
Solubility in water	almost insoluble in water
Hazards
Main hazards	Harmful
Flash point	42 °C
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Cyclopentenone is a hydrocarbon with chemical formula C₅H₆O and CAS number 930-30-3. It is structurally similar to cyclopentanone, with the additional feature of α-β unsaturation in the ring system. Cyclopentenone belongs to the cycloalkene (alkenes which have one or more rings of carbon atoms) class of compounds and is also a ketone (it possesses a carbonyl functional group). It is a liquid at room temperature with a boiling point of 150 °C. It has been isolated from pressure-cooked pork liver by simultaneous steam distillation and continuous solvent extraction.^[1]

The term cyclopentenone may also refer to a structural motif wherein the cyclopentenone moiety is a subsection of a larger molecule. In this regard, cyclopentenones are found in a large number of natural products, including jasmone, the aflatoxins, and several prostaglandins.

Synthesis

Cyclopentenones can be synthesized in a number of ways. Industrially, the most common procedures are elimination of α-bromo-cyclopentanone using lithium carbonate^[2] and Claisen condensation-decarboxylation-isomerization cascades of unsaturated diesters as shown below.^[3]

As a functional group, the synthesis of 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.^[4]

Reactions

As an enone, 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.^[5]

References

1. ^ Mussinan,C.J.; Walradt, J.P. (1974), J. Agric. Food Chem. 22 (5): 827–831, doi:10.1021/jf60195a002 
2. ^ US EP1418166, Daisuke, Fukushima & Hirata Norihiko, "Process for producing 2-bromocyclopentanone", published 2004-05-12 
3. ^ US EP1422212, Liang, Shelue; Andrea Haunert & Sylvia Huber-Dirr et al., "Process for preparing cyclopentenone", published 2004-11-25 
4. ^ Organic Reactions Portal "Cyclopentenone synthesis"
5. ^ Danishefsky, S.; Zamboni, R.; Kahn, M.; Etheredge, S.J. (1980), J. Am. Chem. Soc. 102 (6): 2097–2098, doi:10.1021/ja00526a061