Biomimetic Total Synthesis of (±)-Griffipavixanthone via a Cationic Cycloaddition–Cyclization Cascade

We report the concise, biomimetic total synthesis of the dimeric, Diels–Alder natural product griffi­pavi­xanthone from a readily accessible prenylated xanthone monomer. The key step utilizes a novel inter­molecular [4+2] cycloaddition–cyclization cascade between a vinyl p-quinone methide and an in situ generated isomeric diene promoted by either Lewis or Brønsted acids. Experimental and computational studies of the reaction pathway suggest that a stepwise, cationic Diels–Alder cycloaddition is operative.