Cope rearrangement ring strain

When ring strain is relieved, Cope rearrangements can occur at much lower temperatures and with complete conversion to ring-opened products. A striking example is the conversion of ris-di vinyl cyclopropane to 1,4-cycloheptadiene, a reaction that occurs readily below -40° C.206... 

When the ring strain is relieved, Cope rearrangements occur at much lower temperatures and there is complete conversion to ring opened products. 

In another example, a six-membered ring is expanded to a ten-membered ring by the anionic oxy-Cope rearrangement (Scheme 8.8). The formation of an enolate provides the driving force to overcome the increase in strain energy on going from a six- to ten-membered ring. 

The position of the equilibrium of the Cope rearrangement is pushed even further toward one side when cleavage of the cr bond relieves ring strain. The relief of ring strain also lowers the activation barrier for the rearrangement. For these reasons, d.s-l,2-divinylcyclopropanc is stable only at very low temperatures. 

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