Barton–Zard reaction
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The Barton–Zard reaction is a route to pyrrole derivatives via the reaction of a nitroalkene with an α-isocyanide under basic conditions.[1] It is named after Derek Barton and Samir Zard who first reported it in 1985.[2]
Mechanism
The mechanism consists of five steps:
- Base catalyzed carbonyl enolization of the α-isocyanide.
- 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 aromatisation.
Scope
The nitro compound may be aromatic rather than just an alkene.[3] The reaction has been used for the synthesis of polypyrroles, including porphyrins,[4] as well as dipyrromethenes such as BODIPY.[5]
References
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