Extended Corey–Chaykovsky reactions: transformation of 2-hydroxychalcones to benzannulated 2,8-dioxabicyclo[3.2.1]octanes and 2,3-dihydrobenzofurans

We report the divergent synthesis of benzannulated 2,8-dioxabicyclo[3.2.1]octanes and 2,3-dihydrobenzofurans using the concept of extended Corey–Chaykovsky reactions. With this concept, 2-hydroxychalcones were treated with the Corey ylide providing highly reactive donor–acceptor cyclopropanes that were introduced in a one pot manner for further transformations. We demonstrated that the nucleophilic three-membered ring opening followed by cyclization under mild reaction conditions afforded the 2,8-dioxabicyclo[3.2.1]octane scaffold. On the other hand, heating the intermediates with a strong Brønsted acid furnished 2-phenacyl-2,3-dihydrobenzofurans. These transformations, resulting in products with crucially different heterocyclic skeletons from the same starting compounds, demonstrate the enormous potential of the extended Corey–Chaykovsky reaction.