Nucleophilic Reactions at Tertiary Carbon. Part 2. σ- and π-routes to the 8-hydrindanyl cation

Stereoisomeric ion pairs are implicated as intermediates in the solvolysis of cis and trans-8-hydrindanyl chloride 3 , whereas 4-(cyclopenten-1-yl)butyl tosylate 5 appears to cyclize by way of an unsymmetrically solvated 8-hydrindanyl cation. This follows from the solvolysis products and rates of these compounds in aqueous solvents. The rate and equilibrium constants of the chlorides 3 show that the transition state for the trans-isomer is more stable by 0.5 kcal than the one for the cis-isomer. By inference the intermediates differ by a similar amount of energy. Experimental results are not explained satisfactorily by conformationally isomeric 8-hydrindanyl cations, as suggested in the literature.