Cope Rearrangement

Abstract The thermal isomerization of a 1,5‐diene through the highly stereoselective [3,3] sigmatropic rearrangement leading to a more stable 1,5‐diene is generally known as the Cope rearrangement. The Cope rearrangement can be either thermally or photochemically activated. A few mechanisms have been proposed for this popular rearrangement. Much experimental evidence favors the concerted mechanism. The double allylic alternation and single allylic rearrangement have also been observed. It is reported that when a hydroxyl group appears at position 3 of the 1,5‐diene, the rearrangement rate is extremely accelerated in the presence potassium hydride (KH) and the fast rate for the oxy ‐Cope rearrangement is due to the bond‐weakening effect of the anionic alkoxy group on the adjacent C3‐C4 bond. The rearrangement is found to be even faster when the unsaturation of 1,5‐diene is further extended.