Free-radical reactions of halogenated bridged polycyclic compounds. Part IV. The free-radical addition of polyhalogenomethanes and of thiols to 2,3-dichloronorborna-2,5-diene, and the preparation of 2,3-dichloroquadricyclene

Abstract

The addition of carbon tetrachloride to 2,3-dichloronorborna-2,5-diene (IX) affords the product of 1,2-addition to the unsubstituted double bond, 3-endo,5,6-trichloro-2-exo-trichloromethylnorborn-5-ene (XIIIa), and the product of homoconjugative addition, 5,5,6-trichloro-3-exo-trichloromethylnortricyclene (XIVa); bromotrichloromethane forms the comparable compounds (XIIIb) and (XIVb and/or XVb). The addition of thiols is similar and affords 5,6-dichloronorborn-5-en-2-exo-yl aryl or alkyl sulphides (XIIc, d, and e), together with equal amounts of 5-endo,6-dichloronortricyclyl-3-exo-yl aryl or alkyl sulphides (XIVc, d, and e) and their 5-exo-epimers (XVc, d, and e). The formation of these products is discussed in relation to the free-radical addition reactions of norbornadiene, hexachloronorbornadiene and hexachloromethylenenorbornene, and suggests the importance of nortricyclyl type intermediates in the reactions of the latter two dienes. The preparation of 2,3-dichloroquadricyclene (XVII) is reported.