Cope Elimination
The Cope elimination, developed by Arthur C. Cope, is an elimination reaction that involves the conversion of a tertiary amine to an alkene[1][3]. The reaction begins with the oxidation of a tertiary amine to an intermediate called an "N-oxide" using an oxidant such as hydrogen peroxide[1][6]. This N-oxide, when heated, acts as the base in the elimination reaction[1].
The Cope elimination proceeds through a concerted syn-elimination mechanism. The oxygen from the N-oxide acts as a base, forming an O-H bond, while the C-H and C-N bonds break to form the new C-C pi bond[1]. This reaction mechanism involves an intramolecular 5-membered cyclic transition state, leading to a syn elimination product[3].
Unlike intermolecular E2 reactions, the Cope elimination does not follow Zaitsev’s rule; the major product is always the least stable alkene, i.e., the alkene with the least highly substituted double bond[2]. This is because the basic atom and the beta hydrogen abstracted by it are closest to each other in this conformation[2].
The Cope elimination is a thermal syn elimination; they are thermally activated, unimolecular, and require no acid/base catalysis[1]. This reaction is closely related to the Hofmann elimination, but the base is a part of the leaving group[3].
The Cope elimination is particularly useful when it's easier to perform an elimination reaction when the base is literally next-door (an intramolecular process) as opposed to heating an alkyl halide with a strong base[1]. It should not be confused with the Cope rearrangement, which is a different type of reaction[3][7].
Citations:
[1] https://www.masterorganicchemistry.com/2018/09/24/the-cope-elimination/
[2] https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Reactions/Named_Reactions/Cope_Elimination
[3] https://en.wikipedia.org/wiki/Cope_reaction
[4] https://www.youtube.com/watch?v=hy8d8nXa-Jw
[5] https://www.chemistrysteps.com/the-cope-elimination/
[6] https://www.chadsprep.com/chads-organic-chemistry-videos/cope-elimination/
[7] https://www.chemeurope.com/en/encyclopedia/Cope_reaction.html
[8] https://www.sciencedirect.com/topics/chemistry/cope-elimination
[9] https://www.tutorchase.com/answers/ib/chemistry/what-s-the-mechanism-of-a-cope-elimination
[10] https://en.wikipedia.org/wiki/Cope_rearrangement
[11] https://www.sciencedirect.com/topics/chemistry/cope-reaction