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The Beckmann Rearrangement Alkyl group that migrates does so with retention of configuration, and is always anti to the oxime leaving group N OH N OLVG NH2O H NO Versatile reaction to make lactams and amides Prepared starting from hydroxime, with many leaving groups possible E. Beckmann, Ber. Dtsch. Chem. Ges. 1886, 19, 988.
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Jan 23, 2023 · The Beckmann rearrangement is a reaction discovered in the mid-1880’s by the chemist Ernst Otto Beckmann. The reaction converts oximes into their corresponding amides 1 allowing the insertion of the nitrogen atom from the C=N bond into the carbon chain forming a C–N bond. Depending on the starting material, it could also produce nitriles ...
- Significance of the Beckmann Rearrangement
- Intramolecular or Intermolecular?
- Stereospecificity
- Further Support
- Classic BKR
- Organocatalyzed BKR
- Proposed Mechanism: TsCl
- Organocatalyzed Cyclohexanone Oxime BKR
- Rearrangement Step
Industrial Significance Academic Significance Mechanism still uncertain Illustrated in numerous natural product syntheses Half of all produced cyclohexanone is converted to the oxime for this process. Precursor to nylon-6 Beckmann Rearrangement Publications
Is the migrating carbon group kinetically “free”? Entry of the migrating group into a separate molecule has never been observed Large ring expansion Retention of stereochemistry Unlikely that the ring opened as closure would be prohibitive
FMO Addition of EWG on the oxime oxygen polarizes the LUMO contributions
Carbenium Ion Trapping and Observation R = EWG, fragmentation less favorable (stability of benzylic cation) o-methylacetophenone oxime “More similar to anilinium than phenonium, and concluded to be nitrilium ion..”
Summary Rearrangement is a stereospecific trans shift Rearrangement occurs through an ester-like oxime intermediate (either EWG reagent or autocatalysis) The migrating carbon group is never kinetically free Migration of chiral group does not decrease ee The migration step involves an isomerization followed by ionization to a nitrilium ion intermedi...
First example, advertised as a milder method Proposed mechanism Propose Grob type isomerization but not ionization 5a requires addition of acid to act as a catalyst Other Organocatalysts Lead To Mechanistic Questions Cyclopropenium Promoted Stoichiometric Catalytic In situ generation prior to addition of oxime
Cycle I the more favorable pathway Proposed Mechanism: HCl
Sequestration of nitrilium ion leads to poor conversion Generality of Self-Propagation Mechanism Organocatalyzed BKR
Concerted or Stepwise? Acetophenone: Three step process
Mar 15, 2011 · The rearrangement of a ketoxime to the corresponding amide was discovered in 1886 by E. Beckmann and is known as the Beckmann rearrangement. The rearrangement is brought about by acids, including Lewis acids. The more common rearranging agents are concentrated sulfuric acid, phosphorus pentachloride in ether, and Beckmann's mixture, hydrogen chloride in a mixture of acetic acid and acetic ...
Jan 2, 2024 · In synthetic organic chemistry, the Beckmann rearrangement is quite popular, caprolactam is synthesized from cyclohexanone oxime on a large scale for Nylon-6 production. The function of numerous catalysts and media in the Beckmann rearrangement has been discussed in depth in this review.
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- 02 January 2024
The Beckmann Rearrangement. L. G. Donaruma W. Heldt. Chemistry. 2011. The rearrangement of a ketoxime to the corresponding amide was discovered in 1886 by E. Beckmann and is known as the Beckmann rearrangement. The rearrangement is brought about by acids, including…. Expand. 21. PDF.
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C. Ramalingan, Y.-T. Park, J. Org. Chem., 2007, 72, 4536-4538. Zinc (II) catalyzes a single-step protocol for the Beckmann rearrangement using hydroxylamine- O -sulfonic acid (HOSA) as the nitrogen source in water. This environmentally benign and operationally simple method efficiently produces secondary amides under open atmosphere in a pure ...
