Controllable cyclization of alkynyl thioethers via Brønsted acid-catalyzed dearomatization

An efficient Brønsted acid-catalyzed formal alkyne hydroarylation of phenol-alkynyl thioethers via dearomatization and rearrangement is described. This protocol enables practical and atom-economical synthesis of valuable phenanthrols in generally excellent yields under mild reaction conditions. Moreover, the corresponding dearomatization intermediates could be collected with high efficiency, and the asymmetric version has also been achieved by employing a chiral Brønsted acid as a catalyst.