Free-radical reactions of halogenated bridged polycyclic compounds. Part IX. The addition of methanethiol and bromotrichloromethane to 1,4,7,7-tetrachloronorborn-2-ene, and of bromotrichloromethane to some chlorine-substituted norbornadienes

Abstract

The addition of methanethiol to 1,4,7,7-tetrachloronorborn-2-ene affords 1,4,7,7-tetrachloronorborn-2-endo-yl methyl sulphide, which is formed by endo attack of methylthio-radicals. The addition of bromotrichloromethane gives 3-endo-bromo-1,4,7,7-tetrachloro-2-exo-trichloromethylnorbornane derived from exo attack by trichloromethyl radicals. Similar products derived from exo attack by trichloromethyl radicals are formed in the addition of bromotrichloromethane to 1,2,3,4,7-anti-pentachloronorborna-2,5-diene, and 1,2,3,4-tetrachloronorborana-2,5-diene, and also, very probably, to 1,2,3,4,7,7-hexachloronorborna-2,5-diene and 1,4,7,7-tetrachloro-2,3-bismethylthionorborna-2,5-diene. These results are interpreted as demonstrating that in the addition of free radical reagents to chlorine-substituted norbornadienes and norbornenes, the direction of radical attack, and hence the product structures, are controlled primarily by electronic rather than steric factors. The synthesis of 1,4,7,7-tetrachloronorborn-2-ene via the reductive desulphurisation of 1,4,7,7-tetrachloro-2,3-bismethylthionorborna-2,5-diene is reported.