Carboximidate

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The carboximidate group

Carboximidates (or more general imidates) are organic compounds, which can be thought of as esters formed between a imidic acid (R-C(=NR')OH) and an alcohol, with the general formula R-C(=NR')OR".

They are also known as imino ethers, since they resemble imines (>C=N-) with an oxygen atom connected to the carbon atom of the C=N double bond.[1]

Synthesis

Imidates may be generated by a number of synthetic routes,[2] but are in general formed by the Pinner reaction. This proceeds via the acid catalyzed attack of nitriles by alcohols.

General mechanism of the Pinner reaction[3]

Imidates produced in this manner are formed as their hydrochloride salts, which are sometimes referred to as Pinner salts. Carboximidates are also formed as intermediates in the Mumm rearrangement and the Overman rearrangement.

Imidate/amidate anions

An amidate/imidate anion is formed upon

tautomers, they form the same anion upon deprotonation. The two names are thus synonyms describing the same anion, although arguably, imidate refers to the resonance contributor on the left, while amidate refers to the resonance contributor on the right. However, they are distinguished when they act as ligands for transition metals, with O-bound species referred to as imidates and N-bound species referred to as amidates. They can be considered aza-substituted analogues of enolates
with the formula R-N=C(O−)R.

Imidate/amidate resonance
Imidate/amidate resonance

Reactions

Carboximidates are good

orthoesters
RC(OR)3, aromatic imidates can also be converted but far less readily.

Chapman rearrangement

The Chapman rearrangement is the thermal conversion of aryl N‐arylbenzimidates to the corresponding amides, via intramolecular migration of an aryl group from oxygen to nitrogen.[4] It is named after Arthur William Chapman, who first described it,[5] and is conceptually similar to the Newman–Kwart rearrangement.

Chapman Rearrangement
Chapman Rearrangement

As a protecting group

Benzyl trichloroethanimidate

Carboximidates can act as

TBS protections and may be cleaved by acid hydrolysis.[7]

See also

References

  1. ^ "Pinner Reaction". Organic Chemistry Portal. Buckten, CH: Reto Mueller. Retrieved 2023-09-26.
  2. ^
    doi:10.1021/cr60210a003
    .
  3. ISBN 978-0-471-22854-7
    , S. 516.
  4. ISBN 0471264180
    .
  5. doi:10.1039/CT9252701992
    .
  6. ISBN 978-0-471-69754-1
    .
  7. doi:10.1055/s-1999-2736
    .
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