Indium-Catalyzed Organic Synthesis Techniques

Indium catalysts have emerged as versatile tools in modern organic synthesis, offering mild Lewis acidity combined with remarkable functional‐group tolerance. Indium(III) salts such as InCl₃, InBr₃ and InI₃ efficiently activate unsaturated substrates toward cyclisation, hydroarylation and carbon–carbon bond-forming processes under neutral or slightly acidic conditions. The unique reactivity profile of indium stems from its ability to stabilise nonclassical carbocation intermediates without over-promoting polymerisation or rearrangement. As a result, one-pot sequences that couple indium-mediated cycloisomerisation with subsequent palladium-catalysed cross-coupling via triorganoindium reagents have been developed, enabling the rapid construction of elaborate polycyclic frameworks. Beyond cyclisation chemistry, indium catalysts also promote regioselective allylation, ring-opening of lactones through selective C(sp³)–O bond cleavage and stereoselective cascade processes that deliver complex heterocycles with high atom economy. These methods find broad application in the synthesis of natural products, medicinal scaffolds and fine chemicals, highlighting indium’s role as a sustainable alternative to more aggressive Lewis acids.

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Indium-Catalyzed Organic Synthesis Techniques publication trend

The graph below shows the total number of articles in indium-catalyzed organic synthesis techniques across all publications each year (not limited to Nature Index journals).

Technical terms

Cascade cycloisomerisation: Successive intramolecular cyclisation steps occurring in a single reaction sequence to build polycyclic structures.

Hydroarylation: Addition of an aryl C–H bond and a hydrogen atom across an unsaturated carbon–carbon bond under catalytic activation.

Triorbanoindium reagent: Organometallic species of the general formula R₃In used as a nucleophilic coupling partner in cross-coupling reactions.

6-endo-dig: Nomenclature describing a six-membered ring closure via intramolecular attack on a triple bond with digonal geometry.

Atom economy: Metric reflecting the proportion of reactant atoms incorporated into the desired product, indicating sustainable efficiency.

References

1. Sequential In-catalyzed intramolecular hydroarylation and Pd-catalyzed cross-coupling reactions using bromopropargyl aryl ethers and amines. Organic Chemistry Frontiers (2017).
2. Indium(III)-Catalyzed Stereoselective Synthesis of Tricyclic Frameworks by Cascade Cycloisomerization Reactions of Aryl 1,5-Enynes. The Journal of Organic Chemistry (2021).
3. Regio- and Stereoselective Allylindation of Alkynes Using InBr3 and Allylic Silanes: Synthesis, Characterization, and Application of 1,4-Dienylindiums toward Skipped Dienes. Molecules (2018).
4. Indium-catalysed ring opening of 2-hydroxybutyrolactone through the cleavage of C(sp$^3$)–O bond. Comptes Rendus Chimie (2023).