the effect of the central and external cyclobutane bonds on the modes of the ring expansion of the cyclobutylmethyl moiety. Since the products obtained from the endo tosylate were the olefin and the acetate having 1,7-tetramethylenenorbornane skeleton, it is deduced that the ring expansion occurs selectively to afford [4.3.2]propellan-7-yl cation which is stabilized by the external cyclobutane bond