Inhibition of ring expansion reactions in the norbornane system by neighbouring methyl groups

Abstract

Solvolysis of endo-3,3-dimethylnorborn-2-ylmethyl toluene-p-sulphonate proceeds via a hydride shift without any expansion of the cyclohexane ring, in contrast to the endo-norborn-2-ylmethyl ester, which readily undergoes ring expansion on solvolysis. The amines of both systems, however, give ring expanded products on deamination. The change in mechanism is discussed in terms of the electronic effects of the 3,3-dimethyl substituent. Failure of pinan-10-yl toluene-p-sulphonate to undergo ring expansion is believed to be due to the relative instability of the bicyclo[4.1.1]octane system.