Sequential Wagner–Meerwein rearrangements of polychlorinated complex cations derived from monodechloroisodrin and monodechloraldrin, and the 1H nuclear magnetic resonance spectra of polychloropolycyclic ketones and dechloroaldrin derivatives

Abstract

Monodechloroaldrin and monodechloroisodrin (obtained by selective removal of one of the bridge methylene chlorines from the appropriate hexachlorotetracyclododecadiene) are protonated in acids to give cations which are intercepted by e.g. acetic acid to give the anticipated acetates. In concentrated sulphuric acid on the other hand both dienes are hydrolysed with concomitant transannular ring closure to give the same novel tetrachloropentacyclic ketone (IX) as the initial product. Its unique formation from a common intermediate cation derived by successive Wagner–Meerwein [1,2]shifts in the initial ions formed from the two stereoisomeric dienes is demonstrated. This ketone is readily isomerised in contact with silica gel or mild bases to give a closely related ketone whose structure is established by its unusual ¹H n.m.r. spectrum, the interpretation of which is facilitated by deuterium labelling experiments and LAOCOON 3 computer simulation. The ¹H n.m.r. spectra of intermediates used for synthesis of the deuterium labelled ketones are discussed with special reference to proximity deshielding effects. Mass spectral data for most of the compounds discussed are listed.