Synthesis of Benzofuran-Fused Oxepines through Cs₂CO₃-Promoted [4 + 3] Annulation of Aurones with Crotonate-Derived Sulfonium Salts

Benzofuran-fused derivatives display important and reliable therapeutic properties. Herein, we describe the synthesis of benzofuran-fused oxepines using aurones and crotonate-derived sulfonium salts via a [4 + 3] annulation reaction in the presence of Cs2CO3. This reaction proceeds under mild and operationally simple conditions. The synthetic utility of this approach was highlighted by several transformations, including the efficient synthesis of a novel tetracyclic fused benzofuran derivative.