Indolinone

Indolinone is a family of bicyclic heterocycles consisting of a benzene ring fused to a five‑membered lactam ring that carries a carbonyl group. The term covers both indolin-2-one (2-indolinone) and indolin-3-one (3-indolinone) isomers, depending on whether the carbonyl is at the 2- or 3-position of the five-membered ring. The parent scaffolds are often referred to simply as indolinones, with many substituted derivatives described in the literature.

Structure and properties: The core is a planar, highly conjugated system in which the lactam carbonyl participates in the ring. The nitrogen is part of the lactam, providing a potential site for N-substitution and contributing hydrogen-bonding capacity. Functionalization commonly occurs at the C-2 or C-3 positions of the indolinone ring, as well as on the fused benzene ring, enabling a range of derivatives with varying electronic and steric properties.

Synthesis: Typical routes to indolinones involve cyclization of ortho-aminobenzaldehyde derivatives or related precursors, as well as oxidative cyclization of indoline substrates. These methods can furnish either the 2- or 3-position carbonyl isomer, depending on the reaction conditions and substrates used.

Reactivity and applications: The lactam carbonyl is a reactive functional group for further transformations, and the ring system supports diverse substitutions. Indolinones are widely used as synthetic building blocks in medicinal chemistry, serving as pharmacophore scaffolds for various biological activities. Derivatives have been explored as enzyme inhibitors and anticancer agents, among other applications, and are also employed in materials science and as frameworks for fluorescent probes in some contexts.