Elbs reaction

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The Elbs reaction is an

Elbs oxidation. The reaction was published in 1884.[1][2][3] Elbs however did not correctly interpret the reaction product due to a lack of knowledge about naphthalene
structure.

Scope

The Elbs reaction enables the synthesis of condensed aromatic systems. As already demonstrated by Elbs in 1884 it is possible to obtain anthracene through dehydration. Larger aromatic systems like pentacene are also feasible. This reaction does not take place in a single step but leads first to dihydropentacene that is dehydrogenated in a second step with copper as a catalyst.[4]

Elbs reaction to anthracite and pentacene
Elbs reaction to anthracite and pentacene

The

aluminum chloride.[2][4]

The Elbs reaction is sometimes accompanied by elimination of substituents and can be unsuited for substituted polyaromatics.[5]

Mechanism

At least three plausible mechanisms for the Elbs reaction have been suggested.

cyclisation of the benzophenone, followed by a [1,3]-hydride shift to give the compound . A dehydration reaction
then affords the polyaromatic.

Fieser's mechanism
Fieser's mechanism

Alternatively, in the second mechanism, due to Cook, the methylated aromatic compound instead first undergoes a

tautomerization followed by an electrocyclic reaction
to give the same intermediate, which then similarly undergoes a [1,3]-hydride shift and dehydration.

Cook's mechanism
Cook's mechanism

A third mechanism has also been proposed, involving

pyrolytic
radical generation.

Variations

It is also possible to synthesise

free radical reaction steps.[6]

Heterocyclic Elbs reaction
Heterocyclic Elbs reaction

References

  1. doi:10.1002/cber.188401702247
    .
  2. ^
    doi:10.1002/prac.18860330119
    .
  3. doi:10.1002/0471264180.or001.06
    .
  4. ^
    ISBN 978-3-13-541505-5
    .
  5. ^
    ISBN 9780470638859
    .
  6. doi:10.1039/JR9560003435
    .
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