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.