Catalytic Asymmetric Ring‐Opening Reactions of Unstrained Heterocycles Using Cobalt Vinylidenes

Abstract

Cobalt catalysts promote highly enantioselective ring‐opening reactions of 2,5‐dihydrofurans using vinylidenes. The products are acyclic organozinc compounds that can be functionalized with an electrophile. The proposed mechanism involves the generation of a cobalt vinylidene species that adds to the alkene by a [2 + 2]‐cycloaddition pathway. Ring‐opening then occurs via outer‐sphere β‐O elimination assisted by coordination of a ZnX2 Lewis acid to the alkoxide leaving group. DFT models reveal that competing inner‐sphere syn β‐H and β‐O elimination pathways are suppressed by the geometric constraints of the metallacycle intermediate. These models rationalize the observed stereochemical outcome of the reaction.