Reaction of Strained-Ring Heterocycles with a Rhenium(V) Dioxo Complex

Epoxides and episulfides react stereospecifically with Tp‘ReO₂, generated in situ from Tp‘ReO₃ and PPh₃ (Tp‘ = hydrido-tris(3,5-dimethylpyrazolyl)borate). A combination of direct atom transfer, resulting in alkene, and ring expansion, resulting in a five-member rhenacycle, is observed. When epoxides cis- and trans-cyclooctene oxide are used, the ring-expanded product is exclusively the corresponding Re(V) diolate. However, when an episulfide such as ethylene sulfide or cis- or trans-cyclooctene sulfide is used, the predominant observed rhenium product is a dithiolate. Retention of initial stereochemistry is observed in all cases. Selectivity between atom transfer and ring expansion is measured for each substrate, and a mechanistic model is proposed to account for the reaction outcome.