View source for Barton–Zard reaction

The '''Barton–Zard reaction''' is a route to [[pyrrole]] derivatives via the reaction of a nitroalkene with an α-isocyanide under basic conditions.<ref name= "Li">{{cite book | author =Jie Jack Li | title =Heterocyclic Chemistry in Drug Discovery | publisher =Wiley | location =New York | year =2013
| isbn =9781118354421| url =https://books.google.com/books?id=p_fM6CuK6xcC}} pp.43-4</ref> It is named after [[Derek Barton]] and [[Samir Zard]] who first reported it in 1985.<ref>{{cite journal|last1=Barton|first1=Derek H. R.|last2=Zard|first2=Samir Z.|title=A new synthesis of pyrroles from nitroalkenes|journal=Journal of the Chemical Society, Chemical Communications|date=1985|issue=16|pages=1098|doi=10.1039/C39850001098}}</ref>
[[Image:Barton-Zard reaction.svg|center|450px]]
==Mechanism==
The mechanism consists of five steps:
* Base catalyzed carbonyl [[Keto–enol tautomerism|enolization]] of the α-[[isocyanide]].
* [[Michael reaction|Michael-type addition]] between the α-[[isocyanide]] carbonyl enolate and the nitroalkene.
* 5-endo-dig [[cyclization]] (see: [[Baldwin's rules]]).
* Base catalyzed elimination of the nitro group.
* Tautomerization leading to [[Aromatic compound|aromatisation]].
[[Image:Barton-Zard mechanism corrected.svg|center|650px]]
===Scope===
The nitro compound may be aromatic rather than just an alkene.<ref>{{cite journal|last1=Lash|first1=Timothy D.|last2=Novak|first2=Bennett H.|last3=Lin|first3=Yanning|title=Synthesis of phenanthropyrroles and phenanthrolinopyrroles from isocyanoacetates: An extension of the barton-zard pyrrole condensation|journal=Tetrahedron Letters|date=April 1994|volume=35|issue=16|pages=2493–2494|doi=10.1016/S0040-4039(00)77152-8}}</ref> The reaction has been used for the synthesis of polypyrroles, including [[porphyrins]],<ref>{{cite journal|last1=Finikova|first1=Olga S.|last2=Cheprakov|first2=Andrei V.|last3=Beletskaya|first3=Irina P.|last4=Carroll|first4=Patrick J.|last5=Vinogradov|first5=Sergei A.|title=Novel Versatile Synthesis of Substituted Tetrabenzoporphyrins|journal=The Journal of Organic Chemistry|date=January 2004|volume=69|issue=2|pages=522–535|doi=10.1021/jo0350054|pmid=14725469}}</ref> as well as dipyrromethenes such as [[BODIPY]].<ref>{{cite journal|last1=Ono|first1=Noboru|title=Barton-Zard Pyrrole Synthesis and Its Application to Synthesis of Porphyrins, Polypyrroles, and Dipyrromethene Dyes|journal=Heterocycles|date=2008|volume=75|issue=2|pages=243|doi=10.3987/REV-07-622|doi-access=free}}</ref>
==References==
{{reflist}}
{{Organic reactions}}
{{DEFAULTSORT:Barton-Zard synthesis}}
[[Category:Heterocycle forming reactions]]
[[Category:Name reactions]]