Acetolysis of [n.3.2]Propellane Tosylates

Acetolysis of [n.3.2]propellane tosylates la-d and 2a-d was studied in order to elucidate the steric effect of the third rings in these systems on the acetolysis rates and to synthesize 1,7-methylene-bridged norbomane skeletons. It was found that, in contrast with the case of exo tosylates, the acetolysis rates of endo ones were greatly affected by the nature (rigid or flexible) of the third rings. While the steric deceleration observed for endo-[3.3.2]propellane (1a) was explained in terms of steric hindrance to ionization due to a fairly rigid nature of the third ring, i.e., cyclopentane, the steric acceleration found for endo-[5.3.2]- and endo-[6.3.2]propellane (1c and 1d) was attributed to nonbonded strain in the ground state which might be relieved by ionization without steric strain in the transition state, owing to the flexible nature of the third rings, i.e., cycloheptane and cyclooctane. In most cases, the rearrangement products such as olefins 7a-d and alcohols 9a-d, having 1,7-methylene-bridged norbomane skeletons, which were derived from 1,2-migration of the cyclobutane bond, were obtained in good yields.