Pyrolysis Cope elimination reaction

Pyrolysis of Amine Oxides The Cope Elimination Reaction ... 

Cope elimination reaction. Formation of an olefin and a hydroxylamine by pyrolysis of an amine oxide. 

Pyrolysis of the oxide of tertiary amine 1 yields olefin 2 and hydroxylamine 3. This olefination method is known as the Cope elimination reaction.1-3... 

Pyrolysis of tertiary amine oxides (the Cope elimination reaction) also offers relatively mild reaction conditions (100-200 °C). Oxidation of the tertiary amine... 

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

An even milder cycloelimination uses a ring of five atoms 6.28 instead of six, but still involves six electrons. This is no longer a retro-ene reaction, but it is still a retro group transfer and it is allowed in the all-suprafacial mode 6.29. The pyrolysis of N-oxides 6.30 is called the Cope elimination, and typically takes place at 120°, the corresponding elimination of sulfoxides 6.31 (X=S) typically takes place at 80°, and, even easier, the elimination of selenoxides takes place at room temperature or below. All these reactions are affected by functionality making these numbers only rough guides, but they are all reliably syn stereospecific. 

Cope, A. C., Trumbull, E. R. Olefins from amines the Hofmann elimination reaction and amine oxide pyrolysis. Org. React. 1960,11, 317-493. 

It may be noted that pyrolysis of isoindoline (V-oxides may also furnish isoindoles,32 although in general this is a less useful preparative route since other reactions (deoxygenation, Cope elimination of the 2-substituent) may intervene,6 as shown for the 2-(/J-phenylethyl) derivative in Scheme 2. 

C.iii. Ester Pyrolysis.If the structural components required for syn-elimination in the Hofmann and Cope elimination could be modified to use more readily available synthetic precursors, the reaction might have wider applicability. One possibility is to replace the amino group with an oxygen moiety so there is a... 

Propylthietane (30) occurs as a natural secretion from the stoat. The Hofmann route to racemic (30) from the sulfone (27) by pyrolysis of the quaternary salt (28) gives the sulfone (29) (36%), whereas pyrolysis of the A(-oxide (31) in the presence of N-hydroxypiperidine gives by Cope elimination the isomeric sulfone (32) (58%). The sulfone (29) is converted into (32) under the conditions use in the Cope reaction. The thietane (30) is obtained by reduction of the sulfones (93JHC873). 

This conclusion was supported by the observation that pyrolysis of 3-butenol has a AS of —8.8 eu, which is similar to the activation entropy values reported for pyrolysis of ethyl formate and for 3-butenoic acid, and the activation energies for all three pyrolyses are also similar (about 40 kcal/mol). Another well-known concerted syn elimination is the Cope elimination, which involves the thermal elimination of an alkene from an amine oxide (Figure 10.53). Unlike the reactions discussed above, all of which have... 

The pyrolysis of amine oxides is called Cope elimination and typically takes place at 120 °C (Scheme 6.21). The reaction is a syn periplanar elimination in which six electrons move in a five-membered ring according to a concerted, thermally induced mechanism to yield an alkene and a hydroxylamine. 

In some cases, eliminations occur in non-ionizing solvents and without the addition of any base. In these cases the reactant itself has an internal base and a cyclic transition state leads to elimination. The symbolism for the reactions is Ei, standing for elimination, intramolecular. Only heat is required to induce the reaction, and hence these reactions are called thermal eliminations (the term pyrolysis is also sometimes used). Thioesters, xanthates, selenoxides, and N-oxides are common in these reactions. The Cope elimination involves the formation of an N-oxide and subsequent elimination via the pathway shown in Eq. 10.91, and the Chugaev elimination involves xanthate esters [ROC(S)SR]. The Chugaev elimination was shown to follow a syn elimination pathway based on the stereospecific nature of the reaction (Eqs. 10.92 and 10.93). 

Cope, A.C., Trumbull, E.R. (1975) Olefins from Amines The Hofmann Elimination Reaction and Amine Oxide Pyrolysis in Organic Reactions, RE Krieger Publ. Co., New York. 

Cope, A.C., Mehta, A.S. (1%3) Mechanism of the Hofmann elimination reaction an yUde intermediate in the pyrolysis of a highly branched quaternary hydroxide. Journal of the American Chemical Society, 85, 1949-1952. 

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. 

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