Inductive Effects in Neighboring-Group Participation. Destabilization of Carbocations by CC Double Bonds in Solvolyses of 2,2,5,5-Tetramethylcyclopent-3-en-1-yl Tosylates

Article abstract of DOI:10.1021/jo00250a015

The possibility of homoallylic participation in solvolyses of substituted cyclopent-3-en-1-yl sulfonates has been investigated.Relative rates of solvolyses of 2,2,5,5-tetramethylcyclopentyl (6), 2,2,3,4,5,5-hexamethylcyclopent-3-en-1-yl (13), 2,2,5,5-tetramethyl-3,4-bis(methylene)cyclopent-1-yl (16), and 2,2,5,5-tetramethylcyclopent-3-en-1-yl (18) tosylates in 80percent (v/v) ethanol/water at 95 deg C are 128:5.9:5.4:1.Measures of solvent effects on the reactivity of tetramethylcyclopentyl tosylate 6 (m = 0.88, Q' = 0.94) confirm the expectation that nucleophilic solvent participation (if any) is very week, and the large destabilizing effect of the double bond in the cyclopent-3-en-1-yl cation, predicted by theoretical calculation, is now confirmed experimentally.Diene products arising from 1,2-methyl shifts dominate.Solvolytic data in weakly nucleophilic media (e.g., hexafluoroisopropyl alcohol) show that β-methyl and β,β-dimethyl substitution increase the solvolysis rate of cyclopenyl tosylate cumulatively, but the tetramethyl derivative shows anomalously low reactivity, possibly due to steric inhibition of solvation and of departure of the leaving group.