Cope rearrangement
Abstract
The Cope rearrangement is a [3,3]-sigmatropic rearrangement that converts a 1,5-diene into another 1,5-diene through a pericyclic mechanism. It is the all-carbon analog of the Claisen rearrangement, differing only in the absence of a heteroatom in the reacting framework.
Keywords
1,5-diene, Rearrangement
Category
Rearrangement
Mechanism
Mechanistically, the σ-bond between C3 and C4 of the 1,5-diene breaks and the two 𝜋-bonds (C1=C2 and C5=C6) both shift inward by one position, giving the new 𝜋-bonds at C2=C3 and C4=C5 in the product. As with the Claisen rearrangement, the transition state is preferentially chair-like, though a boat-like transition state is also accessible in constrained systems.
Since the C-C bond that breaks is thermodynamically equivalent to the one that forms, the reaction is generally reversible and the equilibrium depends on steric and electronic factors induced by substituents.
