Intramolecular nucleophilic interception by the sulfonyl group of reaction intermediates arising from electrophilic addition to unsaturated non-conjugated bicyclic sulfones

Abstract

Electrophilic addition of molecular bromine and related reactions to unsaturated bicyclic sulfones resulting in atypical addition is described. 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 stabilising effect, which can be quenched by the presence of water in the reaction media, between the polar SO₂ group and the incipient carbocation centre as depicted in 6. Also described is formal nucleophilic neighbouring group participation by the endo-sited sulfonyl group in norbornylene systems 12 which leads exclusively to the exo,exo-dibromides 13 upon ionic bromination. In the case of unsaturated sulfone 27, bromination to form the exo,exo-dibromide 30 occurs via. decomposition of an isolable, albeit metastable, tribromide salt 29. Owing to a similar effect, treatment of the related exo-epoxide 16 with hydrogen bromide in acetic acid results in the regio- and stereo-specific formation of exo-bromohydrin 17 as the sole product.