Study on syn-dichlorination of alkene via tandem radical additions, vicinal substitutions of activated cyclic intermediates, and double displacements with the assistance of internal nucleophile

Abstract

In contrast to the traditional anti-dichlorinations, syn-dichlorination is considerably less developed. In this study, the development of convenient syn-dichlorination of alkene was investigated with three strategies. The first approach was tandem radical additions. Two types of reagents, cyclic vicinal N,N’-dichlorides and phosphorus(V) dichlorides were designed. However, the preparations of cyclic dichlorides were unsuccessful, and the preparation of phosphorus(V) dichlorides are currently in progress. The second approach was vicinal substitutions of cyclic intermediates by chloride. Unfortunately, reactive [3+2] cycloadduct of nitro group and alkene was not generated under the reaction conditions. On the other hand, vicinal substitutions of cyclic sulfate in the presence of Lewis acids afforded dichlorides in low yields. However, the diastereoselectivities were not satisfactory. The last approach was double displacement with the assistance of an internal nucleophile. As catalyst with a tethered nucleophile, several bis(diphenylphosphino)alkyl oxide sulfide were prepared. However, the catalysts were unstable under the reaction conditions. Although, syn-dichlorination of alkene has not yet been achieved with these strategies, a further study will be conducted with caged phosphorus phosphorus(V) dichloride.