The Cyclopropylcarbinyl‐Cyclobutyl‐Homoallylic Rearrangement. Part III. Evidence for a symmetrical intermediate and for two discrete rearrangement processes

In buffered 70% aqueous dioxane the cyclopropylcarbinyl ( 1 ‐X), endo ‐cyclobutyl ( 2 ‐X) and homoallylic ( 3 ‐X) derivatives (X = nucleofuge) react to give the same mixture of alcohols 1 ‐OH and 3 ‐OH by way of a common intermediate, the symmetrical homoallylic ion 22 . This follows from a study of optically active reactants 1 ‐X and 3 ‐X and from the deuterium scrambling pattern in the products from deuteriated 1 ‐X, endo ‐ 2 ‐X and 3 ‐X. The high solvolysis rates of 3 ‐X indicated π‐bond participation in the transition state, while the high rates of 1 ‐X and endo ‐ 2 ‐X reflect strong σ‐bond participation which is absent in exo ‐ 2 ‐X. Prolonged heating of 1 ‐X, endo ‐ 2 ‐X and 3 ‐X in formic acid leads to a degenerate rearrangement of the initially formed 3 ‐formate. As evidenced by deuterium scrambling, carbon atoms 1, 3 and 7 eventually become positionally equivalent in the latter compound.