Indole

Indole is an aromatic heterocyclic compound consisting of a benzene ring fused to a pyrrole ring. Its scaffold occurs in many natural products and serves as a building block in organic synthesis.

Pyrrole: Pyrrole is a five-membered aromatic ring containing one nitrogen atom. The pyrrole ring supplies indole’s nitrogen and one half of its fused scaffold.
Electrophilic aromatic substitution: Electrophilic aromatic substitution replaces a ring hydrogen with an electrophile while restoring aromaticity. Indole commonly reacts with electrophiles at its electron-rich C3 position.
Tryptophan: Tryptophan is an essential amino acid whose side chain contains an indole group. It is a major biological source of the indole scaffold.
Skatole: Skatole, or 3-methylindole, is an indole derivative produced during microbial breakdown of tryptophan. It is a simple substituted indole associated with intestinal and animal odors.
Benzene: Benzene is a six-membered aromatic ring composed of six carbon atoms. The benzene ring forms the other half of indole’s fused scaffold.
Fischer indole synthesis: The Fischer indole synthesis converts aryl hydrazones of aldehydes or ketones into indoles under acidic conditions. This named reaction is a widely used route for constructing indole rings.
Indole-3-acetic acid: Indole-3-acetic acid is a plant hormone in the auxin family that regulates growth and development. It demonstrates how an indole derivative functions as a natural signaling molecule.
Carbazole: Carbazole is a nitrogen-containing tricyclic aromatic compound with two benzene rings fused to a pyrrole ring. It extends indole’s fused-ring architecture with an additional benzene ring.
Aromaticity: Aromaticity is the unusual stability associated with cyclic, conjugated electron systems. Indole’s fused rings share a conjugated aromatic system.
Madelung synthesis: The Madelung synthesis forms indoles by cyclizing N-acyl-o-toluidines under strongly basic conditions. It builds the fused ring system by intramolecular cyclization.

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