Photocatalytic Dearomative Intermolecular Seven‐Membered Ring Construction of Benzofurans

Abstract

We report the synthesis of seven‐membered carbocycles through the dearomative intermolecular reaction of benzofurans with vinylcyclopropanes. The significant feature of this method involves activating benzofurans through energy transfer from an activated photocatalyst. Substituent effects were investigated for each substrate, and hydrocyclohepta[b]benzofurans with a tetrasubstituted carbon were obtained as a single diastereomer. This synthetic approach compliments the reported methodologies for synthesizing this type of skeleton and introduces a new feedstock for this skeleton with a different substitution pattern. Computational studies of the reaction mechanism suggested that the reaction proceeds stepwise through addition, small ring opening, and re‐cyclization. This novel synthetic approach opens up new possibilities for efficiently constructing seven‐membered carbocycles. Moreover, it provides a valuable platform for discovering unique molecules with diverse substitution patterns.