Article · Wikipedia archive · Last revised Jul 15, 2026

Isoindole

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 are of significant utility and commercial value. Several alkaloids containing this ring system have been isolated from plants.

Last revised
Jul 15, 2026
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Citations
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Source
Wikipedia ↗
Isoindole
Skeletal formula
Skeletal formula source ↗
Ball-and-stick model
Ball-and-stick model source ↗
Names
Preferred IUPAC name
2H-Isoindole1
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
UNII
  • InChI=1S/C8H7N/c1-2-4-8-6-9-5-7(8)3-1/h1-6,9H checkY
    Key: VHMICKWLTGFITH-UHFFFAOYSA-N checkY
  • InChI=1/C8H7N/c1-2-4-8-6-9-5-7(8)3-1/h1-6,9H
    Key: VHMICKWLTGFITH-UHFFFAOYAW
  • c1cccc2c1c[nH]c2
Properties
C8H7N
Molar mass 117.15 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Isoindole is a heterocyclic compound consisting of a benzene ring fused with pyrrole along the carbon-carbon bond furthest from its nitrogen atom.2 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.3 Several alkaloids containing this ring system have been isolated from plants.4

Synthesis

The parent isoindole was prepared by flash vacuum pyrolysis of N-(methoxycarbonyloxy)isoindoline.5

source ↗

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.6 The degree to which the 2H predominates depends on the solvent and on the arrangement of substituents (for isoindole derivatives).7

2H-Isoindole (right) is the predominant tautomer relative to 1H-isoindole (left) source ↗

N-Substituted isoindoles do not tautomerize.

The commercially important phthalimide is an isoindole-1,3-dione with two carbonyl groups attached to the heterocyclic ring.8

See also

See also

References

References

  1. International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 213. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
  2. Gilchrist, T. L. (1987). Heterocyclic Chemistry. Longman. ISBN 0-582-01422-0.
  3. 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. doi:10.1039/c2cs35093a
  4. See for example: Zhang, X.; Ye, W.; Zhao, S.; Che, C. T. (2004). "Isoquinoline and isoindole alkaloids from Menispermum dauricum". Phytochemistry. 65 (7): 929–932. doi:10.1016/j.phytochem.2003.12.004. PMID 15081297.
  5. R. Bonnett and R. F. C. Brown "Isoindole" J. Chem. Soc., Chem. Commun., 1972, 393-395. doi:10.1039/C39720000393
  6. Alan R. Katritzky; Christopher A. Ramsden; J. Joule; Viktor V. Zhdankin (2010). Handbook of Heterocyclic Chemistry. Elsevier. p. 133.
  7. John A. Joule; Keith Mills (2010). Heterocyclic Chemistry. John Wiley & Sons. p. 447.
  8. Radtke, Volker; Erk, Peter; Sens, Benno (2009). "Isoindoline pigments". In Faulkner, Edwin B.; Schwartz, Russell J. (eds.). High Performance Pigments (2nd ed.). Wiley-VCH. pp. 221–241. doi:10.1002/9783527626915.ch14. ISBN 978-3-527-62691-5.