Carbon–carbon bond participation in the solvolysis of exo-2,3-o-arylene-5-norbornyl toluene-p-sulphonates

Abstract

A number of exo-2,3-o-arylene-5-norbornyl toluene-p-sulphonates have been prepared: o-phenylene-[(1a) and (2a)] dimethoxy-o-phenylene-[(3a) and (4a)] and nitro-o-phenylene [(5a) and (6a)]. Rates and products of solvolysis have been studied for solutions in acetic and formic acids. Comparison of the rates of acetolysis of the exo- and endo-toluene-p-sulphonate derivates revealed low exo:endo rate ratios [(1a):(2a), 1·74; (3a):4a), 1·86; (5a):(6a), 1·12]. In formic acid, larger exo:endo rate ratios were observed for the first two pairs of epimers, but only a small change was found for the nitro-substituted derivatives [(1a):(2a), 11·4; (3a):(4a), 9·4; (5a):6a), 2·1]. Although a similar product distribution was found for the solvolyses of compounds (1a) and (3a) and compounds (2a) and (4a), significant differences were found in the products from compounds (5a) and (6a). The results are explained in terms of weak carbon–carbon bond participation, which does not affect the rate of solvolysis of compounds (1a) and (3a) in acetic acid, but which does play some part in the control of product formation. The changes in exo:endo rate ratio on changing the medium to formic acid are interpreted as resulting from an increase in the importance of carbon–carbon bond participation. The changes in the degree of this participation with changes in substitution in the aromatic ring and change in medium are discussed. In view of the results obtained for solvolysis of the endo-derivatives (2a), (4a), and (6a) it is suggested that k_Δ and k_s processes cannot be completely independent, and ‘leakage’ apparently occurs.