Acid‐Promoted Cascade Cyclization to Produce 2‐(4′‐alkoxyaryl)‐3,4‐fused Tricyclic Dihydrobenzopyrans Via a Vinylidene Para‐quinone Methide Intermediate

We developed a novel method for synthesizing 2‐(4‐hydroxyaryl)‐3,4‐fused tricyclic dihydrobenzopyrans with 2,3‐syn and 3,4‐syn motif based on the acid‐promoted cascade cyclization via vinylidene para‐quinone methide intermediates. Using easily prepared linear substrates, TFA‐promoted cascade cyclization proceeded in the presence of triethylsilane, affording a series of five to seven‐membered ring‐fused dihydrobenzopyran derivatives in moderate to excellent yield in a highly diastereoselective manner. The developed method provided new access to potent and selective ERβ agonists.