Abstract

Indole is an electron-rich heteroaromatic nitrogen heterocycle which is isolated from coal-tar distillate. The chemistry of indole is dominated by electrophilic substitution reactions which occur primarily at the 3-position. Organometallic derivatives, especially lithium compounds, permit reactions at other ring positions. Substituted indoles are usually prepared from benzene derivatives having a nitrogen substituent. Indole derivatives appear prominently in nature, usually as metabolites of tryptophan. Examples include plant alkaloids and fungal metabolites. Synthetic derivatives of indole have been extensively explored as pharmaceuticals; the nonsteroidal antiflammatory drug indomethacin is the most widely used example.