Cope reaction

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.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite encyclopedia</ref>

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:<ref>Template:Cite journal</ref>

synthesis of methylenecyclohexane

Mechanism and related eliminations

The reaction proceeds through the E_i pathway, with an intramolecular, cyclic 5-membered transition state.^{{{#if:|{{{2}}}|[1]}}} 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.)<ref>Template:Cite book</ref><ref>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 {{#invoke:doi|main}}</ref><ref>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. {{#invoke:doi|main}}</ref>

File:CopeReactionJACS82-4656.svg

This organic reaction is closely related to the Hofmann elimination,^{{{#if:|{{{2}}}|[2]}}} 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.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> The reaction is a form of hydroamination and can be extended to the use of unsubstituted hydroxylamine, in which case oximes are produced.<ref>Template:Cite journal</ref>