Brønsted Acid‐Catalyzed Regioselective [7+1] Annulation for the Construction of Indole‐Fused Oxa‐Eight‐Membered Rings

ABSTRACT A Brønsted acid‐catalyzed regioselective [7+1] annulation of α ‐aryl‐ γ ‐( α ‐indolyl)phenols with aromatic aldehydes has been developed for the synthesis of indole‐fused eight‐membered oxacycles. In this transformation, α ‐aryl‐ γ ‐( α ‐indolyl)phenols function as 1,7‐bis‐nucleophiles, whereas aromatic aldehydes serve as readily available one‐carbon bis‐electrophiles. The reaction proceeds under metal‐free conditions with broad substrate scope, good functional‐group compatibility, and high regioselectivity. This protocol provides an efficient and practical approach to indole‐fused eight‐membered heterocycles and highlights the utility of aldehydes as versatile building blocks for medium‐sized ring synthesis.