REARRANGEMENTS OF SPIROCYCLOBUTANE-SUBSTITUTED 2-NORBORNYL CATIONS

2-Norbornyl cations with spiroannellated cyclobutane rings were genera ted for comparison with the previously studied cyclopropane analogues. Starting with the Diels-Alder reaction of cyclopentadiene with methyl enecyclobutan, piro-[bicyclo[2.2.1]heptane-2,1'-cyclobutan]-6-one (11) was prepared. The tosylhydrazone 12 of 11 was photolyzed in NaOD/D2O to give the analogous alcohol 13 with a ca. 1:1 distribution of deuter ium. Ring expansion was not observed, in contrast to the cyclopropane analogue. - The tosylhydrazone 22 of spiro[bicyclo[2.2.1]heptane-2,1'- cyclobutan]-3-one (21) and the related tosylates (28, 32) rearranged, in part, to afford derivatives of spiro[bicyclo[2.2.1]heptane-7,1'-cyc lobutane] (29, 33, 34). In both series, ring expansion of the spiroann ellated cyclobutane, by exo-3,2-C shift, was the major reaction, givin g rise to a uniquely endo-selective tertiary cation (36). Analogously positioned cyclopropane rings remain intact, due to stabilizing intera ctions with the neighboring positive charge which are lacking in the c yclobutane systems. - In CDCl3 solution, the tosylate 32 produced mixt ures of isomeric tosylates by way of ion pair recombination. We observ ed that exo --> exo shifts of the counterion proceed with little scram bling of O-18 whereas complete equilibration of the tosylate oxygens i s attained in exo --> endo shifts.