Chapman rearrangement

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The Chapman rearrangement is a name reaction in organic chemistry first reported by Mumm and his co-workers in 1915. It was extensively researched by AW Chapman in the 1920s and 1930s. It is a thermal rearrangement of aryl imino esters to carboxamides :

Chapman rearrangement using the example of an O- phenylimino ester; Ar denotes aromatic radicals , these can be the same or different.

mechanism

The following illustration shows a plausible mechanism of this reaction using the example of an O- phenylimino ester (Ar = aryl group, identical or different). The Chapman rearrangement occurs in both polar and non-polar solvents . However, it is favored in polar solvents.

Mechanism of the Chapman rearrangement, Ar denotes aromatic radicals, these can be the same or different.

If the aryliminoester 1 is heated , the nitrogen atom attacks the phenyl ring nucleophilically. This deflavorized characterized and it forms a Spirointermediat 2 . The spirointemediate 2 then reacts with rearomatization to form the diaryl amide 3 .

It follows approximately first order reaction kinetics . The Chapman rearrangement has applications in the manufacture of N -arylamides.

Abnormal Chapman rearrangement

If the migrating aryl radical has a substituent in the ortho position that has an acidic H atom in the α-position to the aryl radical , a so-called “abnormal” Chapman rearrangement can occur. This is the case, for example, if a methyl acetate radical has been substituted on the migrating aryl group (see 4 ) in the ortho position . This example explains the mechanism of the "abnormal" Chapman rearrangement:

Course of the abnormal Chapman reaction, Ar denotes aromatic residues, these can be the same or different.

An acidic α-H atom is split off from the methyl acetate group of the imino ester 4 . The resulting carbanion 5 intramolecularly attacks the partially positively charged carbon atom of the iminoester 5 . Phenolate 6 is produced in an intermediate step (rotation around a CC bond) . In acidic work-up, this splits off methanol and thus becomes the benzofuran derivative 7 .

See also

Individual evidence

  1. ↑ a b c d after: Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , p. 627.
  2. ↑ Michael B. Smith: March's Advanced Organic Chemistry. 7th edition, Wiley & Sons, 2013, ISBN 978-0-470-46259-1 , pp. 1428-1429.
  3. ↑ a b after: Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , p. 628.
  4. ↑ John W. Schoolsberg, S. Archer: An Abnormal Chapman Rearrangement . In: Journal of the American Chemical Society . tape 82 , no. 8 , 1960, pp. 2035–2038 , doi : 10.1021 / ja01493a046 .