Synthesis of 1,4-Naphthoquinone Methides via Acid-Catalyzed Cascade Cyclizations of Benzannulated Enediynyl Alcohols

Treatment of benzannulated enediynyl alcohols with trifluoroacetic acid at room temperature promoted a cascade sequence of cyclization reactions, leading to 1,4-naphthoquinone methides. The transformation involved an unusual two-carbon ring expansion from the cyclic alcohols and the construction of the p-quinone methide ring from an acyclic system along the reaction pathway.