Abstract: The preparation of the previously unknown cis-1-methylcyclopropylcarbinyl cation 3 is reported. Cation 3 rearranges rapidly at-100 OC to the stable trans isomer, but instead of a direct rotation of the Ca-C1 bond, 3 finds a lower energy route involving at least seven intermediates, including the observable 1-ethylally1 cation 5.
