Free-radical reactions of halogenated bridged polycyclic compounds. Part V. The addition of thiols and bromotrichloromethane to 1,2,3,4-tetrachloro-7,7-dimethoxynorborna-2,5-diene and the preparation of 1,2,3,4-tetrachloro-7,7-dimethoxyquadricyclene

Abstract

The free-radical addition of thiols to 1,2,3,4-tetrachloro-7,7-dimethoxynorborna-2,5-diene (Ia) affords 1,4,5,6-tetrachloro-7,7-dimethoxynorborn-5-en-2-endo-yl alkyl sulphides (IV) and 1,2,3,5-endo-tetrachloro-6,6-di-methoxynorborn-2-en-7-syn-yl alkyl sulphides (V). Bromotrichloromethane affords 5-exo-bromo-1,2,3,5-endo-tetrachloro-6,6-dimethoxy-7-syn-trichloromethylnorborn-2-ene (XI) as sole product. The results are compared with those of similar reactions of hexachloronorbornadiene (Ib), and it is concluded that the large steric size of the C-7 substituents controls the direction of radical attack. Methoxy-substituents at C-7 appear to retard chain transfer with thiols less than chlorine substituents: the reverse situation applies for chain transfer with bromotrichloromethane. The preparation of 1,2,3,4-tetrachloro-7,7-dimethoxyquadricyclene (XII) is reported.