Conformation and reactivity in the bicyclo [3.3.2] decane system

Abstract

The synthesis of a series of substituted bicyclo (3.3.2) decane derivatives is described. Infra-red spectroscopy shows the presence of bands that can only be ascribed to a 3,7-interaction in a twin-chair conformation for many derivatives, but there is evidence for a conformational equilibrium between twin-chair and boat-chair conformations. In cases where the atoms of the two carbon bridge are constrained by a double bond, or an equivalent grouping, so that they are coplanar with the bridgehead atoms, the preferred conformation is the boat-chair; this has been confirmed by the X-ray structure of 7,8,9,10-tetrahydro-6,10-propano-6H-cyclohepta(b)quinoxaline. Solvolytic studies on exo-2,3-epoxybicyclo(3.3.2)decane are reported. Hydride shifts are found to be more facile than in the bicyclo(3.3.1)nonane system, and a revised mechanistic scheme for the acid catalysed solvolysis of epoxides is described. Buffered acetolysis of exo-2-bicyclo(3.3.?)decyl tosylate shows two interesting phenomena. Firstly, there appears to be a significant 1,2-hydride shift to the bridgehead position, and secondly, it is probable that a 2,6- hydride shift is taking place in a twin-twist-boat conformation. 9-Bicyclc(3.3.2)decanone has been found to be a surprisingly unreactive ketone; this lack of reactivity is rationalised in terms of I-strain theory. Preliminary studies into the autoxidation of bicyclo(3.3.2)decane and the synthesis of bicyclo(3.3.2)deca-2,6-diene are reported, the latter in connection with a study into the Single Inversion Cope Reaction.