Relative Reactivity of Bridgehead Adamantyl and Homoadamantyl Substrates from Solvolyses with Heptafluorobutyrate as a Highly Reactive Carboxylate Leaving Group. Absence of SN2 Character of Solvolysis of tert-Butyl Derivatives

Article abstract of DOI:10.1021/ja00306a019

Heptafluorobutyrates, conveniently prepared from alcohols, possess a reactivity similar to that of halides in solvolysis reactions.A product and isotope distribution study for the reaction of 1-adamantyl heptafluorobutyrate (1a) in 80:20 ethanol-H2(18)O demonstrated exclusive alkyl-oxygen cleavage.The reactivities of 1a, 1-(2a), and 3-homoadamantyl heptafluorobutyrate (3a) increase with the flexibility of the hydrocarbon skeleton.The rate constants are linearly correlated with the strain increase upon ionization.No acceleration attributable to nucleophilic solvent assistance was evidenced for the tert-butyl ester, 4a.A literature proposal for such assistance in solvolyses of 4 is examined.The existing data are explained better by an S_N1 process with electrophilic assistance of the leaving group in the solvents that can form very strong hydrogen bonds.