Synthetic Approaches to Indene Derivatives

Indene derivatives, characterised by a benzene ring fused to a five-membered cyclopentene, occupy a central place in modern synthetic chemistry owing to their prevalence in pharmaceuticals, agrochemicals and advanced materials. Constructing the indene core demands precise control of ring formation and substitution patterns. Classical approaches rely on electrophilic aromatic cyclisations, typified by Friedel–Crafts strategies, which assemble the five-membered ring via Lewis-acid activation of suitably substituted precursors. Transition-metal catalysis, especially palladium- and gold-mediated annulations, has broadened the scope, enabling [3+2] cycloadditions and cascade sequences under milder conditions. Radical-initiated processes and hydrogen-shift triggered tandem reactions deliver multifunctionalised indenic frameworks in streamlined, often one-pot formats. More recently, the incorporation of fluorinated groups—particularly trifluoromethyl substituents—has attracted attention for tuning bioactivity and physicochemical properties, prompting the development of both de novo CF3-indene syntheses and selective trifluoromethylation of preformed indane cores. Collectively, these methods underscore the versatility of indene synthesis and its growing impact across chemical biology and materials science.

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Synthetic Approaches to Indene Derivatives publication trend

The graph below shows the total number of articles in synthetic approaches to indene derivatives across all publications each year (not limited to Nature Index journals).

Technical terms

Indene: Bicyclic hydrocarbon comprising a benzene ring fused to a cyclopentene.

Friedel–Crafts cyclisation: Electrophilic aromatic substitution using a Lewis acid to form new carbon–carbon bonds.

Propargyl cation: Carbocation intermediate derived from ionisation of a propargyl alcohol, stabilised by alkyne conjugation.

Trifluoromethylation: Introduction of a CF3 group into an organic molecule to alter electronic and lipophilic properties.

Annulation: Ring-forming reaction that constructs a cyclic structure through bond-forming events such as cycloadditions or coupling.

Hydroindolation: Acid-promoted intramolecular cyclisation that forges the indane framework via protonation and C–C bond formation.

References

1. Synthetic approaches to multifunctional indenes. Beilstein Journal of Organic Chemistry (2011).
2. Tandem processes promoted by a hydrogen shift in 6-arylfulvenes bearing acetalic units at ortho position: a combined experimental and computational study. Beilstein Journal of Organic Chemistry (2016).
3. TfOH-Promoted Reaction of 2,4-Diaryl-1,1,1-Trifluorobut-3-yn-2-oles with Arenes: Synthesis of 1,3-Diaryl-1-CF3-Indenes and Versatility of the Reaction Mechanisms. Molecules (2018).
4. Dispersion-Controlled Regioselective Acid-Catalyzed Intramolecular Hydroindolation of cis-Methindolylstyrenes To Access Tetrahydrobenzo[cd]indoles. Organic Letters (2019).
5. Synthesis of 1-Trifluorometylindanes and Close Structures: A Mini Review. Organics (2021).