The reaction of some chloride-substituted norbornadienes and norbornenes with sodium thiomethoxide

Abstract

The reaction of 1,2,3,4,7,7-hexachloronorborna-2,5-diene and related norbornadienes containing a dichloro-substituted 2,3-double bond, with sodium thiomethoxide in dimethylformamide as solvent, results in successive replacement of the vinylic double-bond chlorines. The corresponding 1,2,3,4,7,7-hexachloronoroborn-2-ene and related norbornenes are less reactive, and only with norbornenes containing at least one bridge chlorine is it possible to isolate even a monosubstitution product. Aldrin does not react, and isodrin gives a low yield of monosubstitution product. Competitive studies suggest that replacement of vinylic chlorines is aided to a comparable degree by both an unsubstituted double bond, and by bridge chlorines. Bridgehead chlorines have less effect on reactivity. The rate-determining step of reaction is likely to be attack by thiomethoxide ions on the chlorine-substituted double bond. The disubstitution product 1,4,7,7-tetrachloro-2,3-dithiomethoxynorborna-2,5-diene derived from hexachloronorbornadiene deteriorates on keeping, for more than 2 weeks, to afford 1,4,7,7-tetrachloro-2,3,5-endo-trithiomethoxynorborn-2-ene. This compound is also formed in the hydrogen chloride catalysed addition of methanethiol to 1,4,7,7-tetrachloro-2,3-dithiomethoxynorborna-2,5-diene, whereas in the freeradical catalysed addition it is only a minor product formed together with the major product 1,5-endo-6,6-tetrachloro-2,3,7-syn-trithiomethoxynorborn-2-ene.