Solvolysis of bicyclo[3,2,1]octan-3-yl p-toluenesulphonates

Abstract

The solvolytic mechanisms for the pair of bicyclo [3, 2, 1] octan-3-yl tosylates (1 and 2) have been investigated in buffered acetic and formic acids, and in some aqueous alcoholic mixtures. The rate constants, and α- and β-d4 kinetic isotope effects were measured, and the products were analysed. [diagram shown (1)] [diagram shown (2)]

The α-effects are fairly high (1.16-1.20) and not very solvent dependent, and are therefore compatible with a mechanism involving little solvent nucleophilic participation. The β-d4 effects are very high (1.93-2.75) for both isomers, suggesting that participation by these neighbouring carbon-hydrogen bonds is involved in the ionization of these compounds. A non-chair transition state is proposed for the exo tosylate (2), in parallel with results for many other cyclic systems with (initially) equatorial leaving groups.1,2 The product analyses for both isomers show predominant inversion of configuration, and varying amounts of rearranged products. The similarity in the rearranged products, and in their relative proportions from both tosylates suggests that a common non-classical carbonium ion intervenes in the rearranged product forming steps from both diastereoisomers. This ion appears to be similar to that implicated in the solvolysis of trans-bicyclo [3, 2, 1] octan-2-yl derivatives.3 The hypothesis that nucleophilic participation by solvent or by neighbouring groups or bonds occurs in most solvolysis reaction is made, and allows a new interpretation of some recent literature results.