Diastereoselective functionalisation of benzo-annulated bicyclic sultams: Application for the synthesis of cis-2,4-diarylpyrrolidines

The cis-dibromination of unsaturated bicyclic bridgehead sultams 5a and 5b, and experiments designed to understand the cis-stereochemical outcome of these reactions, are described. In the case of 5b, a novel solvent dependent carbocation rearrangement occurs with the formation of 18b. cis-Dibromides 13a and 13b undergo regioselective dehydrobromination, and the participation of the resultant vinyl bromide 24a in lithiation and Pd-coupling chemistry is described. In the case of the latter, hydrogenation of the styryl products afforded a single diastereoisomer. These compounds were then studied under dissolved metal reduction conditions, in which the cleavage of both N-S and C-S bonds takes place to afford cis-2,4-diaryl-substituted pyrrolidines 35-37.