Barton Zard Synthesis
Encyclopedia
The Barton-Zard Synthesis method of pyrrole
synthesis is a cyclisation reaction between a nitroalkene and α-isocyanoacetate under base conditions.
Pyrrole
Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. It is a colourless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., N-methylpyrrole, C4H4NCH3...
synthesis is a cyclisation reaction between a nitroalkene and α-isocyanoacetate under base conditions.
Mechanism
It consists in three main steps:- Michael-type addition between the α-isocyanideIsocyanideAn isocyanide is an organic compound with the functional group -N≡C. It is the isomer of the related cyanide , hence the prefix iso....
carbonyl enolate and the nitroalkene. - Cyclization between isocyanide's carbeneCarbeneIn chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is RR'C:, but the carbon can instead be double-bonded to one group. The term "carbene" may also merely refer to the compound H2C:, also called...
and the anion formed in the α position of nitroNitro-Chemistry:*Nitroglycerin, an explosive chemical compound*Nitromethane, the simplest organic nitro compound; also used to fuel high-performance internal-combustion engines*Nitrous oxide, "laughing gas", used in some dental procedures as an anaesthetic...
group. - Elimination of nitro group with consecuent aromatization.