Cross and parallel cyclisation–rearrangement of face proximate π-2p-C cations generated in polycyclic olefins

Abstract

Partially dechlorinated and other derivatives of the cyclodiene pesticides have been made and their behaviour in strongly acid media investigated with a view to correlating structure with cyclisation geometry. The X-ray crystal structure of one key compound unambiguously indicates that in the absence of the dichloromethano-bridge characteristic of the parent pesticides aldrin and isodrin, cross rather than parallel cyclisation is preferred in strongly acid conditions. Successive thermal rearrangements of 1,2,3.4-tetrachlorocyclopentadiene used here in synthesis of useful model compounds is briefly discussed together with certain other acid-catalysed transformations of isodrin and dieldrin analogues. Simple Hückel MO calculations accord with experimental observation.