Deamination of bicyclo[2.2.2]octan-2-yl- and bicyclo[3.2.1]octan-2-yl-amines. Evidence for classical precursors of non-classical carbonium ions

Abstract

Bicyclo[2.2.2]octan-2-yl- and exo-bicyclo[3.2.1]octan-2-yl-amines have been deaminated in acetic acid by nitrous acid and via their N-phenyltriazenes; their ethyl N-nitrosocarbamates have also been solvolysed in ethanol. Product distributions by a given method from the structurally Isomeric starting materials are similar to each other and to the common product distribution obtained from bicyclo[2.2.2]-octane-2-yl and exo-bicyclo[3.2.1]octan-2-yl toluene-p-sulphonates. Each amine gives, however, a small but unmistakable excess of the structurally unrearranged product compared (in the case substitution) with the distribution obtained from the solvolysis of the corresponding bicyclo-octyl toluene-p-sulphonates. Each amine gives, however, a small but unmistakable excess of the structurally unrearranged product compared (in the case of substitution)with the distribution obtained from the solovolysis of the corresponding bicyclo-octyl toluene -p-sulphonates. endo-Bicyclo[3.2.1]octan-2-ylamine has also been deaminated in acetic acid by nitrous acid and via its ethyl N-nitrosocarbamate in ethanol. The product ratios of these reactions are characteristically different from those of the isomeric amines but, as far as substitution is concerned, are similar to what is obtained from endo-bicyclo[3.2.1]octan-2-yl toluene-p-sulphonate. A common mechanism describe all the deaminative reactions. We propose that classicalcarbonium ions are the initial products of fragmentation of diazo-intermediates. These are intercepted to only a small extent to give products structurally and sterochemically characteristic of the original amines; to an even smaller extent they rearrange to isomeric classical carbonium ions is rearrangement to non-classical isomers. From both classic carbonium ion is produced as has been implicated in the solvolysis of the corresponding toluene-p-sulphonates. endo-Bicyclo[3.2.1]octan-2-ylamine deamination gives rise to an isomeric symmetrical non-classical carbonium ion, the same one that intervenes in the solvolysis of endo-bicyclo[3.2.1]octan-2-yl toluene-p-sulphonate. Symmetrical and unsymmetrical non-classical carbonium ions once formed give product ratio largely independent of their origins or modes of formation although the symmetrical one appears to undergo a small extent of isomerization to the (more stable) unsymmetrical species. These result are contrasted with those obtained from simple carbocyclic system (without branching at the β-carbon)in which deamination and toluene-p-sulphonate solovolysis give characteristically different and unrelated product distributions.