Molar mass 82.04 g/mol Density 980 kg/m³ | Formula C5H6O Boiling point 150 °C | |
 | ||
2-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. 2-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.
Contents
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
2-Cyclopentenones can be synthesized in a number of ways. Industrially, the most common procedures are elimination of α-bromo-cyclopentanone using lithium carbonate and Claisen condensation-decarboxylation-isomerization cascades of unsaturated diesters as shown below.
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.
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.