INTRAMOLECULAR NUCLEOPHILIC INTERCEPTION BY THE SULFONYL GROUP OF REACTION INTERMEDIATES ARISING FROM ELECTROPHILIC ADDITION TO UNSATURATEDNONCONJUGATED BICYCLIC SULFONES

Electrophilic addition of molecular bromine and related reactions to u nsaturated bicyclic sulfones resulting in atypical addition is describ ed. Bromination of the bicyclic sulfone 3 results in a ca. 1:1 mixture of exo,exo- and exo,endo-dibromides 4 and 5, respectively. Similarly, acid-catalysed cleavage of epoxide 8 produces a 37:63 mixture of exo, exo- and exo,endo-bromohydrins 9 and 10, respectively. In both cases, formation of exo,exo-products is explained in terms of a favourable st abilising effect, which can be quenched by the presence of water in th e reaction media, between the polar SO, group and the incipient carboc ation centre as depicted in 6. Also described is formal nucleophilic n eighbouring group participation by the endo-sited sulfonyl group in no rbornylene systems 12 which leads exclusively to the exo,exo-dibromide s 13 upon ionic bromination. In the case of unsaturated sulfone 27, br omination to form the exo,exo-dibromide 30 occurs via decomposition of an isolable, albeit metastable, tribromide salt 29. Owing to a simila r effect, treatment of the related exo-epoxide 16 with hydrogen bromid e in acetic acid results in the regio- and stereo-specific formation o f exo-bromohydrin 17 as the sole product.