Polyfluoro-heterocyclic compounds. Part XI. Factors controlling the orientation of nucleophilic substitution in octafluoro-3,3′-bipyridyl and related compounds

Abstract

Octafluoro-3,3′-bipyridyl can be obtained by the Ullmann synthesis and reacts with alkoxides in the corresponding alcohols to give 4- and 6-substituted compounds, the orientation being dependent both on the nucleophile and the solvent. Methyl-lithium and ammonia in ether lead exclusively to 6-substitution. From these results, and disubstitution with methoxide, it is concluded that the orientation of substitution is affected both by steric requirements of the nucleophile and the polarity of the medium and this is rationalised in terms of relative charge-delocalisation in the transition states, and possibly by interaction of the reagent with the ring-nitrogen. It is shown that the steric requirements of alkoxide ions are very dependent on solvent.