Free-radical reactions of halogenated bridged polycyclic compounds. Part XI. Application of the Cristol–Firth reaction to some carboxylic acids containing a chloronorbornene ring system

Abstract

The Cristol-Firth reaction has been applied to a number of carboxylic acids containing a chloronorbornene ring system. 1,4,5,6,7,7-Hexachloronorborn-5-en-2-ylacetic acid affords, via the 1,4,5,6,7,7-hexachloronorborn-5-en-2-ylmethyl radical, the corresponding 1,4,5,6,7,7-hexachloronorborn-5-en-2-ylmethyl halides. 1,4,5,6,7,7-Hexachloronorborn-5-en-2-ylcarboxylic acid gives the 1,4,5,6,7,7-hexachloronorborn-5-en-2-yl radical, which may undergo chain transfer from both the exo- and endo-directions to afford the corresponding halides. If the halogen is bromine rearrangement to the 2,3,3,4,5,6-hexachloronorborn-5-en-2-yl radical competes with chain transfer, and this new radical can additionally afford products on chain transfer with bromine. Reactions with other chloronorborn-5-en-2-ylcarboxylic acids are similar. Evidence is presented that chloronorborn-5-en-2-yl radicals are unlikely to be planar, and are more probably represented by equilibrating exo- and endo-radicals, with the exo-radical being favoured due to minimised nonbonded interactions.