Isoindole is a heterocyclic compound consisting of a benzene ring fused with pyrrole along the carbon-carbon bond furthest from its nitrogen atom. The compound is an isomer of indole. Isoindoline is a hydrogenated form of isoindole. The parent compound is rarely encountered in the literature, but its derivatives (notably phthalocyanine dyes) are of significant utility and commercial value.Heugebaert, Thomas S. A.; Roman, Bart I.; Stevens, Christian V. "Synthesis of isoindoles and related iso-condensed heteroaromatic pyrroles" Chemical Society Reviews 2012, volume 41, pp. 5626-5640. Several alkaloids containing this ring system have been isolated from plants.See for example:
Synthesis The parent isoindole was prepared by flash vacuum pyrolysis of N-(methoxycarbonyloxy)isoindoline.R. Bonnett and R. F. C. Brown "Isoindole" J. Chem. Soc., Chem. Commun., 1972, 393-395.
N-Substituted isoindoles, which are more stable than the parent compound, can be prepared by dehydration of isoindoline-N-oxides. Other starting materials, including o-xylylene dibromide (o-C6H4(CH2Br)2), may be used in their synthesis.
Structure and tautomerism of 2-H-isoindoles Unlike indole, isoindoles exhibit noticeable alternation in the C-C bond lengths, which is consistent with their description as pyrrole derivatives fused to a butadiene.
In solutions, the 2H-isoindole tautomer predominates. It resembles a pyrrole more than a simple imine. The degree to which the 2H predominates depends on the solvent and on the arrangement of substituents (for isoindole derivatives).
N-Substituted isoindoles do not tautomerize.
Isoindole-1,3-diones and related derivatives The commercially important phthalimide is an isoindole-1,3-dione with two carbonyl groups attached to the heterocyclic ring.
See also
1,3-Disubstituted Isoindolines. Isoindene with nitrogen replaced by a methylene group.
References