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Knorr Pyrrole Synthesis

Fischer indole synthesis   Named Reactions in Organic Synthesis
Reaction category:
Heterocycle formation

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In 1886 L. Knorr heated a mixture of alpha-nitroso ethyl acetoacetate and ethyl acetoacetate together in glacial acetic acid in the presence of zinc dust to form a tetra-substituted pyrrole. Since then the condensation of an alpha-amino ketone or alpha-amino- beta ketoester with an active methylene compound is known as the Knorr pyrrole synthesis.

The Neber rearrangement can be used to prepare the precursor alpha-aminoketones from the corresponding oxime by reaction with tosyl chloride.

The alpha-aminoketones are often quite labile and can undergo self-condensation forming a pyrazine so they are often prepared by first nitrosating the ketone and then reducing it in situ.

An anti-inflammatory analgesic compound, 4,5,8,9-tetrahydro-8-methyl-9-oxothieno[3’3’:5,6]cyclohepta[1,2-b]-pyrrole-7-acetic acid was synthesized by H.E. Rosenberg and R.W. Ward utilizing the Knorr pyrrole synthesis.

Mechanism of the Knorr pyrrole synthesis:

mechanism of Knorr pyrrole synthesis

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Other reaction categories:

Pericyclic and photochemical reactions NEW!

Radical reactions

Electrophilic aromatic substitution

Nucleophilic substitution reactions

Transition metal-catalyzed couplings


Reactions involving carbonyl compounds

Reduction reactions

Rearrangement reactions

Electrophilic addition reactions

Some relevant Alfa Aesar products for the Knorr pyrrole synthesis:
Ethyl acetoacetate, 99+%
Acetic acid, glacial, 99+%
Acetic acid, glacial, ACS, 99.7+%
Zinc powder, average 4-7 micron, 97.5% (metals basis)
Zinc powder, -100 mesh, 97+%
Zinc powder, -100 mesh, 99.9% (metals basis)
p-Toluenesulfonyl chloride, 98%
Sodium hydrosulfite, tech., 85+%

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