Cope reaction

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Cope reaction
Named after Arthur C. Cope
Reaction type Elimination reaction
Identifiers
Organic Chemistry Portal cope-elimination
RSC ontology ID RXNO:0000539

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

Contents

Cope reaction CopeReaction.png
Cope reaction

Typically, the amine oxide is prepared from the corresponding amine with a peroxy acid or comparable oxidant. The actual elimination requires just heat.

Illustrative is a synthesis of methylenecyclohexane: [5]

synthesis of methylenecyclohexane MethyleneCyclohexaneByCopeReaction.svg
synthesis of methylenecyclohexane

The reaction proceeds through the Ei pathway, with an intramolecular, cyclic 5-membered transition state. Consequently, the elimination product is always syn and rarely occurs with 6-membered rings. (Rings with 5 or 7 or more members undergo the reaction just fine.) [6] [7] [8]

CopeReactionJACS82-4656.svg

This organic reaction is closely related to the Hofmann elimination, but the base is a part of the leaving group. Sulfoxides can undergo an essentially identical reaction to produce sulfenic acids, which is important in the antioxidant chemistry of garlic and other alliums. Selenoxides likewise undergo selenoxide eliminations.

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 Research Articles

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In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or in the terminal position. Terminal alkenes are also known as α-olefins.

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<span class="mw-page-title-main">2,3-sigmatropic rearrangement</span> Class of chemical reaction

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<span class="mw-page-title-main">Amine oxide</span> Chemical compound containing the functional group R3N→O

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<span class="mw-page-title-main">White catalyst</span> Chemical compound

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In organic chemistry, the Davis oxidation or Davis' oxaziridine oxidation refers to oxidations involving the use of the Davis reagent or other similar oxaziridine reagents. This reaction mainly refers to the generation of α-hydroxy carbonyl compounds (acyloins) from ketones or esters. The reaction is carried out in a basic environment to generate the corresponding enolate from the ketone or ester. This reaction has been shown to work for amides.

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A hydrocupration is a chemical reaction whereby a ligated copper hydride species, reacts with a carbon-carbon or carbon-oxygen pi-system; this insertion is typically thought to occur via a four-membered ring transition state, producing a new copper-carbon or copper-oxygen sigma-bond and a stable (generally) carbon-hydrogen sigma-bond. In the latter instance (copper-oxygen), protonation (protodemetalation) is typical – the former (copper-carbon) has broad utility. The generated copper-carbon bond (organocuprate) has been employed in various nucleophilic additions to polar conjugated and non-conjugated systems and has also been used to forge new carbon-heteroatom bonds.

References

  1. Cope, Arthur C.; Foster, Theodore T.; Towle, Philip H. (1949). "Thermal Decomposition of Amine Oxides to Olefins and Dialkylhydroxylamines". Journal of the American Chemical Society . 71 (12): 3932–3935. doi:10.1021/ja01180a014.
  2. Cope, Arthur C.; Towle, Philip H. (1949). "Rearrangement of Allyldialkylamine Oxides and Benzyldimethylamine Oxide". Journal of the American Chemical Society . 71 (10): 3423–3428. doi:10.1021/ja01178a048.
  3. Cope, Arthur C.; Pike, Roscoe A.; Spencer, Claude F. (1953). "Cyclic Polyolefins. XXVII. cis- and trans-Cycloöctene from N,N-Dimethylcycloöctylamine". Journal of the American Chemical Society . 75 (13): 3212–3215. doi:10.1021/ja01109a049.
  4. Peter C. Astles; Simon V. Mortlock; Eric J. Thomas (1991). "The Cope Elimination, Sulfoxide Elimination and Related Thermal Reactions". Comprehensive Organic Synthesis. Vol. 6. pp. 1011–1039. doi:10.1016/B978-0-08-052349-1.00178-5. ISBN   978-0-08-052349-1.
  5. Cope, Arthur C.; Ciganek, Engelbert (1963). "Methylenecyclohexane and N,N-Dimethylhydroxylamine Hydrochloride". Organic Syntheses . 4: 612. doi:10.15227/orgsyn.039.0040.
  6. March, Jerry; Smith, Michael B. (2007). March's advanced organic chemistry: reactions, mechanisms, and structure (6th. ed.). Wiley-Interscience. p.  1525. ISBN   978-0-471-72091-1.
  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 doi : 10.1021/ja01502a053
  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. doi : 10.1021/ja01502a052
  9. Ciganek, Engelbert; Read, John M.; Calabrese, Joseph C. (September 1995). "Reverse Cope elimination reactions. 1. Mechanism and scope". The Journal of Organic Chemistry. 60 (18): 5795–5802. doi:10.1021/jo00123a013.
  10. Ciganek, Engelbert (September 1995). "Reverse Cope elimination reactions. 2. Application to synthesis". The Journal of Organic Chemistry. 60 (18): 5803–5807. doi:10.1021/jo00123a014.
  11. Beauchemin, André M.; Moran, Joseph; Lebrun, Marie-Eve; Séguin, Catherine; Dimitrijevic, Elena; Zhang, Lili; Gorelsky, Serge I. (8 February 2008). "Intermolecular Cope-Type Hydroamination of Alkenes and Alkynes". Angewandte Chemie. 120 (8): 1432–1435. Bibcode:2008AngCh.120.1432B. doi:10.1002/ange.200703495.