Indolines

Indolines are a class of heterocyclic compounds consisting of a benzene ring fused to a saturated five-membered nitrogen-containing ring. The parent structure, indoline (also called 2,3-dihydroindole), is a bicyclic system in which the five-membered ring is non-aromatic due to saturation at the 2–3 positions, and the nitrogen bears a hydrogen (N-H) or can be substituted. The overall formula is C8H9N. Substituted indolines, including N-alkyl or N-aryl derivatives, as well as substitutions at the 2- and 3-positions, expand the scaffold used in chemical synthesis and medicinal chemistry.

Nomenclature and related compounds: Indoline is the standard name for the 2,3-dihydro derivative of indole. The class also encompasses various N-substituted indolines and 2-,3-disubstituted variants, which are common targets in synthetic methods and drug discovery.

Properties and reactivity: The nitrogen in indolines is a secondary amine, enabling typical amine chemistry such as alkylation and acylation. The fused ring system imparts conformational rigidity, which is valuable for construct design. A key synthetic relationship exists with indoles: hydrogenation of indoles yields indolines, while oxidation of indolines can regenerate indoles. This interconversion makes indolines useful building blocks and intermediates in organic synthesis.

Applications and occurrence: Indoline cores appear in various natural products and are widely used as scaffolds in medicinal chemistry to explore structure–activity relationships. They serve as versatile precursors for the synthesis of more complex alkaloids and pharmaceuticals, and their functionalizable nitrogen atom provides convenient handles for diversification.