Editing Pyrrole (section)

===Cyclization reactions===
Pyrroles with ''N''-substitution can undergo [[cycloaddition]] reactions such as [4+2]-, [2+2]-, and [2+1]-cyclizations. Diels-Alder cyclizations can occur with the pyrrole acting as a diene, especially in the presence of an electron-withdrawing group on the nitrogen. Vinylpyrroles can also act as dienes.{{citation needed|date=July 2016}} 
[[File:Pyrrole DA.svg|center|class=skin-invert-image|300px|Pyrrole DA]]

Pyrroles can react with [[carbene]]s, such as [[dichlorocarbene]], in a [2+1]-cycloaddition. With [[dichlorocarbene]], a dichlorocyclopropane intermediate is formed, which breaks down to form [[3-Chloropyridine|3-chloropyridine]] (the Ciamician–Dennstedt rearrangement).<ref>{{cite journal|last1=Ciamician |first1=G. L. |last2=Dennstedt |first2=M. |title=Ueber die Einwirkung des Chloroforms auf die Kaliumverbindung Pyrrols |trans-title=On the reaction of chloroform with the potassium compound of pyrrole |journal=Berichte der Deutschen Chemischen Gesellschaft  |volume=14 |pages=1153–1162 |date=1881 |url=https://babel.hathitrust.org/cgi/pt?id=hvd.cl1hza;view=1up;seq=1223 |doi=10.1002/cber.188101401240}}</ref><ref>{{cite book|last=Corwin |first=Alsoph Henry |editor-first=Robert Cooley |editor-last=Elderfield |title=Heterocyclic Compounds |volume=1 |location=New York, NY |publisher=Wiley |date=1950 |page=309}}</ref><ref>{{cite book|last=Mosher|first=H. S.  |editor-first=Robert Cooley |editor-last=Elderfield |title=Heterocyclic Compounds |volume=1 |location=New York, NY |publisher=Wiley |date=1950 |page=475}}</ref> 
[[File:Ciamician-Dennstedt Rearrangement.png|500px|center|class=skin-invert-image|Ciamician–Dennstedt rearrangement]]