Amine Oxides Cope Elimination

Oxidation converts the tertiary amine to an amine oxide. Cope elimination ean give either of two alkenes. We expeet the less-hitxlered elimination to be favored, giving the Hofmann produet. 

SCHEME 6.21 Pyrolytic iyn-eliminations in amine oxides Cope elimination. 

Amines as Leaving Groups The Hofmann Elimination 904 Mechanism 19-4 Hofmann Elimination 904 19-15 Oxidation of Amines The Cope Elimination 907... 

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)... 

However, when the temperature is increased to 120°C, the principal reaction is the elimination to olefin. The thermal decomposition of dimethyl dodecyl amine oxide at 125°C in a sealed system, as opposed to a vacuum used by Cope and others, produces 2-methyl-5-decyhsoxa2ohdine, dimethyl dodecyl amine, and olefin (23). The amine oxide oxidi2es XW-diaLkylhydroxylainine to the nitrone during the pyrolysis and is reduced to a tertiary amine in the process. 

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. 

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]. 

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). 

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

In an analogous way, secondary amines can be protected through attachment of / -cyanoethyl or a similar function. The cyanoethyl group undergoes facile Cope elimination from initially formed A-oxide (e.g. 137, equation 91) thus giving the corresponding hydroxylamine 138 in a good yield . ... 

Oxidation of organonitrogen compounds is an important process from both industrial and synthetic viewpoints . N-oxides are obtained by oxidation of tertiary amines (equation 52), which in some cases may undergo further reactions like Cope elimination and Meisenheimer rearrangement . The oxygenation products of secondary amines are generally hydroxylamines, nitroxides and nitrones (equation 53), while oxidation of primary amines usually afforded oxime, nitro, nitroso derivatives and azo and azoxy compounds through coupling, as shown in Scheme 17. Product composition depends on the oxidant, catalyst and reaction conditions employed. 

When 3-phenyl-l,2,4-triazine (411) reacts with the enamine (406), orientation B is followed. In this case the 3,4-dihydropyridine (412) is formed and is isolated. Elimination of the amine directly is unfavourable, because of the cis orientation, and transfer of the proton to the pyridine nitrogen is impossible. Oxidation to the (V-oxide (413) and Cope elimination affords the condensed pyridine (414) (78UP21900). 

A. C. Cope and E. R. Trumbull, "Olefins from Amines. The Flofmann Elimination Reaction and Amine Oxide Pyrolysis," Organic Reactions 11, 317 (1960). 

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