Английская Википедия:Cope reaction

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Шаблон:Distinguish Шаблон:Reactionbox The Cope reaction or Cope elimination, developed by Arthur C. Cope, is an elimination reaction of the N-oxide to form an alkene and a hydroxylamine.[1][2][3][4]

Mechanism and applications

The reaction mechanism involves an intramolecular 5-membered cyclic transition state,Шаблон:Ref leading to a syn elimination product, an Ei pathway. This organic reaction is closely related to the Hofmann elimination,Шаблон:Ref but the base is a part of the leaving group. The amine oxide is prepared by oxidation of the corresponding amine with an oxidant such as meta-chloroperoxybenzoic acid (mCPBA). The actual elimination just requires heat.

Cope reaction
Cope reaction
Шаблон:Clear-left

Illustrative of the Cope reaction is a synthesis of methylenecyclohexane:[5]

synthesis of methylenecyclohexaneШаблон:Clear-left

Piperidines are resistant to an intramolecular Cope reaction[6][7][8] but with pyrrolidine and with rings of size 7 and larger, the reaction product is an unsaturated hydroxyl amine. This result is consistent with the 5-membered cyclic transition state.

intramolecular Cope reactionШаблон:Clear-left

Reverse reaction

The reverse or retro-Cope elimination has been reported, in which an N,N-disubstituted hydroxylamine reacts with an alkene to form a tertiary N-oxide.[9][10] The reaction is a form of hydroamination and can be extended to the use of unsubstituted hydroxylamine, in which case oximes are produced.[11]

Related processes

Sulfoxides can undergo an essentially identical reaction to produce sulfenic acids which is important in the antioxidant chemistry of garlic and other plants of the genus Allium. Selenoxides likewise undergo selenoxide eliminations. Other Ei reactions proceed similarly.

References

Шаблон:Reflist Шаблон:Alkenes Шаблон:Organic reactions

  1. Шаблон:Cite journal
  2. Шаблон:Cite journal
  3. Шаблон:Cite journal
  4. Шаблон:Cite encyclopedia
  5. Шаблон:Cite journal
  6. Шаблон:Cite book
  7. Amine Oxides. VIII. Medium-sized Cyclic Olefins from Amine Oxides and Quaternary Ammonium Hydroxides Arthur C. Cope, Engelbert Ciganek, Charles F. Howell, Edward E. Schweizer J. Am. Chem. Soc., 1960, 82 (17), pp 4663–4669 Шаблон:Doi
  8. Amine Oxides. VII. The Thermal Decomposition of the N-Oxides of N-Methylazacycloalkanes Arthur C. Cope, Norman A. LeBel; J. Am. Chem. Soc.; 1960; 82(17); 4656-4662. Шаблон:Doi
  9. Шаблон:Cite journal
  10. Шаблон:Cite journal
  11. Шаблон:Cite journal