Editing Cyclopentadiene (section)

===Sigmatropic rearrangement===
The hydrogen atoms in cyclopentadiene undergo rapid [[sigmatropic reaction|[1,5]-sigmatropic shifts]]. The hydride shift is, however, sufficiently slow at 0&nbsp;°C to allow alkylated derivatives to be manipulated selectively.<ref>{{cite journal |last1=Corey |first1=E. J. |last2=Weinshenker |first2=N. M. |last3=Schaaf |first3=T. K. |last4=Huber |first4=W. |year=1969 |title=Stereo-controlled synthesis of prostaglandins F-2a and E-2 (dl)|journal=Journal of the American Chemical Society |volume=91 |issue=20 |pages=5675–5677 |doi=10.1021/ja01048a062 |pmid=5808505}}</ref> 
[[File:Prostaglandin Diels-Alder Corey (cropped2).png|400 px|thumb|center|Diene-selective Diels–Alder reaction in Corey's total synthesis of prostaglandin F2α]]

Even more [[fluxional molecule|fluxional]] are the derivatives C<sub>5</sub>H<sub>5</sub>E(CH<sub>3</sub>)<sub>3</sub> (E = [[silicon|Si]], [[germanium|Ge]], [[tin|Sn]]), wherein the heavier element migrates from carbon to carbon with a low activation barrier.