The search for persistent cyclobutylmethyl cations in superacidic media and observation of the cyclobutyldicyclopropylmethyl cation

Primary and secondary cyclobutylmethyl cations were found to be elusive in superacidic media even at low temperatures. They give thermodynamically mor e stable rearrangement products, i.e., the dimeric bicyclo[4.4.0]dec-l-yl c ation and substituted cyclopentyl cations, respectively. In the search for a persistent cyclobutylmethyl cation, the more stabilized cyclobutyldicyclo propylmethyl cation was prepared from its corresponding alcohol in FSO3H/SO 2ClF at -90 degrees C. Using variable-temperature C-13 NMR studies and theo retical calculations, the ion was shown to exist preferentially in its bise cted conformation at -80 degrees C. The ion is predominantly classical, wit h expected significant delocalization into the neighboring cycloalkyl rings .