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Willgerodt rearrangement

Chemical reaction

Willgerodt rearrangement

Chemical reaction

The Willgerodt rearrangement or Willgerodt reaction is an organic reaction converting an aryl alkyl ketone, alkyne, or alkene to the corresponding amide by reaction with ammonium polysulfide, named after Conrad Willgerodt. The formation of the corresponding carboxylic acid is a side reaction resulting from hydrolysis of the amide. When the alkyl group is an aliphatic chain (n typically 0 to 5), multiple reactions take place with the amide group always ending up at the terminal end.

-- The net effect is thus migration of the carbonyl group to the end of the chain and oxidation.

General scheme for the Willgerodt rearrangement

An example with modified reagents (sulfur, concentrated ammonium hydroxide and pyridine) is the conversion of acetophenone to 2-phenylacetamide and phenylacetic acid

The Willgerodt rearrangement using acetophenone

Willgerodt–Kindler reaction

Karl Kindler The related Willgerodt–Kindler reaction{{cite journal

The Kindler modification of the Willgerodt rearrangement

A possible reaction mechanism for the Kindler variation is depicted below:

The likely reaction mechanism for the Kindler modification.

The first stage of the reaction is basic imine formation by the ketone group and the amine group of morpholine to give an enamine. This reacts as a nucleophile with electrophilic sulfur, similar to an Stork enamine alkylation reaction. The actual rearrangement reaction takes place when the amine group attacks the thiocarbonyl in a nucleophilic addition temporarily forming an aziridine and the thioacetamide by tautomerization.

References

References

  1. (1887). "Ueber die Einwirkung von gelbem Schwefelammonium auf Ketone und Chinone". Berichte der Deutschen Chemischen Gesellschaft.
  2. (1888). "Ueberführung von Ketonen und Aldehyden in Säuren und Säureamide mittelst gelben Schwefelammoniums". Berichte der Deutschen Chemischen Gesellschaft.
  3. (1946). "The Willgerodt and Kindler Reactions. III. Amides from Acetylenes and Olefins; Studies Relating to the Reaction Mechanisms". Journal of the American Chemical Society.
  4. (1946). "The Willgerodt Reaction". Organic Reactions.
  5. ''The Willgerodt Reaction. II. A Study of Reaction Conditions with Acetophenone and Other Ketones''DeLos F. DeTar and Marvin Carmack ''[[J. Am. Chem. Soc.]]'' '''1946''', ''68(10)'', 2025 - 2029. ({{doi. 10.1021/ja01214a047)
  6. [[Organic Syntheses]], Coll. Vol. 9, p.99 ('''1998'''); Vol. 74, p.257 ('''1997'''). ([http://www.orgsynth.org/orgsyn/pdfs/CV9P0099.pdf Article])
  7. ''Name Reactions and Reagents in Organic Synthesis'' Bradford P. Mundy, Michael G. Ellerd, Frank G. Jr. Favaloro '''2005''' {{ISBN. 0-471-22854-0
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