A polar substituent effect on the ring-cleavage rearrangement of 1-arylcyclobutylmethyl Grignard reagents

Article abstract of DOI:10.1016/0022-328X(93)80060-O

The kinetics of the ring-cleavage rearrangements of 1-phenylcyclobutylmethylmagnesium chloride and its p-methyl and p-chloro analogs have been determined.The first-order rate constants are correlated by the Hammett equation, with ρ=-0.47.The results are consistent with a concerted mechanism with a cyclic transition state having significant polar character, although polar effects on the stabilities of reactant and product may also contribute.The phenyl group itself slows the reaction by a factor of 0.031, which is interpreted principally in terms of steric destabilization of the transition state.