Ring-opening of hindered cyclic epoxides with potassium carboxylates in the presence of conjugate acids
During attempts to ring-open a highly hindered epoxide, traditional methods were found to be ineffective. An alternative strategy for opening epoxides was implemented that employed a potassium carboxylate in the presence of its conjugate acid in a solvent mixture containing polar and potassium-sequestering components. A systematic analysis of the components of the reaction mixture indicated that the addition of the conjugate acid was the most important feature for providing good conversion. This reaction appears to be general for most classes of carboxylic acids including cinnamic, aromatic, and highly hindered carboxylic acids (30%-79% yield) and only fails with weak carboxylate nucleophiles. Three highly substituted and hindered cyclohexene oxide derivatives were examined for reactivity and the reaction conditions appear to tolerate a variety of functional groups to provide the ring-opened species. This pH-moderate system proved useful for hindered cyclic epoxides when all other techniques failed and should prove general to a wide spectrum of epoxide and carboxylic acid partners in those cases where the use of a strong Lewis or protic acid catalyst, or a strong basic nucleophile, is inappropriate. © 2013 Published by NRC Research Press.