ZnBr₂‑Mediated Cascade Reaction of <i>o</i>‑Alkoxy Alkynols: Synthesis of Indeno[1,2‑<i>c</i>]chromenes

A Lewis acid-mediated cascade annulation of o-alkoxy alkynols in the presence of ZnBr2 has been developed. The cascade cyclization proceeds through a 5-exo-dig cyclization followed by a Friedel–Crafts reaction and ring-opening sequence to synthesize indeno­[1,2-c]­chromenes. This protocol provides a broad substrate scope in moderate to good yields with high regioselectivity. The reaction with benzo-fused cycloalkyl ketones gave an unexpected alkyne C–C bond cleavage resulting in fused polycycles.