Cope eliminations

Cope Elimination- elimination of R2NOH from an amine oxide... 

Elimination. Ahphatic amine oxides having an ahphatic hydrogen P to the nitrogen form olefins and diaLkyl hydroxylamines when heated. This reaction is known as the Cope elimination (17)... 

Some Cope rearrangements and Cope eliminations Claisen or Cope rearrangement Ester cracking Conia ene reaction... 

Amine oxides 2, which can be prepared by oxidation of amines 1, react upon heating to yield an olefin 3 and a hydroxylamine 4. This reaction is called the Cope elimination reaction,and as a synthetic method is a valuable alternative to the Hofmann degradation reaction of quaternary ammonium salts. 

Certain amine oxides, especially those derived from six-membered heterocyclic amines e.g. N-methylpiperidine oxide, that cannot go through a planar, five-membered transition state, do not undergo the Cope elimination reaction. 

In addition to being a valuable method for the preparation of olefins, the Cope elimination reaction also gives access to iV,A -disubstituted hydroxylamines. 

The preparation of an alkene 3 from an amine 1 by application of a /3-elimination reaction is an important method in organic chemistry. A common procedure is the Hofmann elimination where the amine is first converted into a quaternary ammonium salt by exhaustive methylation. Another route for the conversion of amines to alkenes is offered by the Cope elimination. 

Preparation of 3-vinylindole (84) via Cope elimination of N,N-diethyltrypt-amine-N-oxide has been reported [87], An alternate approach based on the Wittig reaction of the readily accessible N-phenylsulfonylindole-3-carbalde-hyde failed because cleavage of the sulfonyl protecting group easily produced an anion whose neutralization led to polymerization [86]. 

The C isotope effects for the Cope elimination (17-8) show that both the C—H and C—N bonds have been extensively broken in the transition state. 

Sulfonium compounds (—C— SR2) undergo elimination similar to that of their ammonium counterparts (17-6 and 17-7) in scope and mechanism but this reaction is not of great synthetic importance. These syn-elimination reactions are related to the Cope elimination (17-8) and the Hofmann elimination (17-6). ... 

When 1,5-dienes are heated, they isomerize, in a [3,3] sigmatropic rearrangement known as the Cope rearrangement (not to be confused with the Cope elimination reaction, 17-8)When the diene is symmetrical about the 3,4 bond, we have the unusual situation where a reaction gives a product identical with the starting material ... 

The action of iV-methylhydroxylamine on enantiopure 4-formylazetidin-2-ones bearing an N-tethered alkynyl group 89 has been studied and products formed by 1,3-dipolar cycloaddition and reverse Cope elimination isolated, e.g. 90 <00TL1647>. 

Oxidations of a range of p-cyanoethyl tertiary amines (44) with m-CPBA in CH2CI2 give the corresponding A-oxides (45), which can be isolated or undergo Cope elimination affording hydroxylamines (46) in high yields (Scheme 2.16) (Table 2.1) (96). Hydroxylamines (46) can be easily oxidated into nitrones (see Section 2.2.1.3). 

Table 2.1 Synthesis of secondary hydroxylamines via Cope elimination of...

In order to study the mechanism of reverse Cope elimination reactions in the condensation of pentenal and hexenal with iV-methylhydroxylamine. it seemed reasonable to synthesize unsaturated nitrones (226). 

Another approach is based on the condensation of lithiated sulfones to unsaturated nitrones (387). Good yields of single stereoisomers of unsaturated hydrox-ylamines (388) are obtained. They undergo a reverse-Cope elimination leading to a single enantiomer of pyrrol idine-/V -oxide (389) (Scheme 2.169) (626). 

Cope Elimination oxidize 3° amine to tertiary ammonium oxide (R N -< V I. heat produces RHC=CH2... 

In 1998, an uncatalyzed cydization of N-2,3-dienylhydroxylamine affording bicyc-lic products was also observed. The reaction was believed to proceed via a reverse Cope elimination [171]. 

This reaction sequence illustrates how the rates of many base-catalyzed reactions can be enhanced greatly by substitution of dimethylsulfoxide for the usual hydroxylic solvents. Other examples of the enhanced reactivity of anions in dimethylsulfoxide are found in Wolff-Kishner reductions and Cope elimination reactions. The present reaction illustrates the generation of an aryne intermediate from bromobenzene. ... 

Cope, A. C. Foster, T. T. Towle, P. H. J. Am. Chem. Soc. 1949, 71, 3929. Arthur Clay Cope (1909-1966) was born in Dunreith, Indiana. He was a professor at MIT when he discovered the Cope elimination reaction and the Cope rearrangement. The Arthur Cope Award is a prestigious award in organic chemistry from the American Chemical Society. 

In the Cope elimination, thirty percent hydrogen peroxide, H2O2, is used to produce an cimine oxide, which upon heating undergoes elimination. This is a syn-elimination process. Figure 13-45 illustrates the general reaction, while Figure 13-46 shows the mechanism of the syn-elimination step. 

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