2-Cyclopenten-1-one

2-Cyclopentenone contains two functional groups, a ketone and an alkene. It is a colourless liquid. 2-cyclopenten-1-one selectively induces the expression of the 70-kDa HSP (HSP70) in human cells through cycloheximide-sensitive activation of heat shock transcription factor 1 (HSF1). It is a natural product found in Perilla frutescens[1].

clear yellow liquid

2-Cyclopenten-1-one is a versatile electrophile employed in various addition reactions including conjugate addition of organocopper nucleophiles, Michael reaction with silyl enol ethers and siloxanes. It is also used in Diels-Alder cycloadditions and phosphoniosilylations.

ChEBI: 2-cyclopenten-1-one is an enone that is cyclopentanone having a C=C double bond at position 2. It has a role as a Hsp70 inducer. It is an enone and an alicyclic ketone.

2-Cyclopentenones can be synthesized in a number of ways. One of the routes involves elimination of α-bromo-cyclopentanone using lithium carbonate and Claisen condensation-decarboxylation-isomerization cascades of unsaturated diesters 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 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.
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[1] A Rossi, M G Santoro, G Elia. “2-Cyclopenten-1-one, a new inducer of heat shock protein 70 with antiviral activity.” The Journal of Biological Chemistry 271 50 (1996): 32192–6.