Synthetic Studies on Penitrem E: Model Studies for the Construction of D/E/F/G-Ring System

Synthetic studies toward the indole diterpene penitrem E are described. A functionalized o-alkynylaniline derivative was designed as a model substrate to construct the D/E/F/G tetracyclic core bearing an exocyclic functional group on the F ring as a precursor for C18 oxygen installation. The tetracyclic compound is furnished through a Pd-catalyzed cascade cyclization of the o-alkynylaniline derivative, which involves indole formation, an intramolecular Heck reaction, and oxidative chlorination of the Heck intermediate.