Structure and Reactivity of Indolylmethylium Ions: Scope and Limitations in Synthetic Applications

What is it about?

Indolylmethylium Ions are stable carbenium ions which can be isolated in high yields. Their reactions with a wide range of nucleophiles produce important indole derivatives. The rate-constants of these second-order reactions have been determined and used to determine the electrophilicities of these cationic indolium intermediates. Their electrophilicity is comparable to that of unsaturated iminium ions and of structurally related diaryl methylium ions. These data can be used to rationally design new reactions with indolylmethylium ions by choosing nucleophiles with appropriate nucleophilic reactivity.

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Why is it important?

Indolylmethylium ions are important electrophilic species in organic synthesis but their electrophilic reactivity was unknown up to date. Quantitative spectrophotometric measurements of their reaction rates with a wide array of nucleophiles allowed to determine their electrophilicities and to compare them with reference electrophiles such as iminiums ions and other carbenium ions,