Polar Effects in the Homoallylic Rearrangement of Arylcyclopropylcarbinols

The synthesis of some p‐substituted phenylmethylcyclopropylcarbinols of the structure (I) is herein reported. Dehydration of the cyclopropylcarbinols by means of acetic anhydride yielded mixtures of α‐cyclopropylstyrenes (V) and 4‐arylpent‐3‐enyl acetates (VI) the ratio of which depended on both the polar characteristics of the substituent X and on reaction conditions. The relative order of the effect of substitution in the phenyl group on V/VI ratio is Cl > H > CH3 > OCH3. The data presented being interpreted in terms of stability of the cyclopropylbenzylium ions (III). The more stable carbonium ions (III or IV) would favor the formation of rearranged products (VI) whereas the less stable would favor the production of V.