Catalytic Ring Opening of Epoxides by Metal Triflates: Influence of a Pending Olefin

Lewis acid-catalyzed epoxide openings efficiently promote intramolecular cyclizations forming complex oxygenated frameworks. Herein, we investigated the reactivity of epoxyolefins under catalytic conditions using various metal triflates. The study focuses on the competition between epoxide isomerization and intramolecular cyclization involving a pendant olefin. Screening of several metal triflates revealed that Lewis superacids, particularly Bi(OTf)₃, promote efficient transformations at room temperature with low catalyst loadings (1 mol%). Structural variation in the substrates significantly influenced product distribution likely through coordination effects, impacting cyclization efficiency with higher yields observed for non-chelating epoxyolefins. Substrates derived from geraniol underwent selective cyclization to cis-cyclic alcohols and bicyclic ethers in good yields, with stereochemical outcomes consistent with the Eschenmoser model. Reaction conditions such as temperature and catalyst loading further modulated selectivity, allowing control over product distribution. These results highlight the potential of metal triflates as versatile and efficient catalysts for the stereoselective intramolecular cyclization of epoxyolefins, offering access to cyclic frameworks under mild conditions.