First Total Synthesis of Dioncophylline B, a 7,6′-Coupled Naphthylisoquinoline Alkaloid

The total synthesis of dioncophylline B (2), a naphthylisoquinoline alkaloid with the rare 7,6′-coupling type and high antimalarial and fungicidal activities, is described. The key step of this convergent synthesis is the regioselective intermolecular biaryl coupling of its appropriately modified naphthalene and isoquinoline moieties, with MOM-functionalized oxygen substituents next to the coupling sites: The naphthalene moiety is activated by a directed ortho-metalation → stannylation procedure, while the isoquinoline part is metalated and then brominated ortho to the MOM-protected oxygen function, thus allowing a Stille coupling to connect the two parts. The work constitutes the first synthesis of any 7,6′-coupled naphthylisoquinoline alkaloid.

dioncophylline B - naphthylisoquinoline alkaloids - total synthesis - cross coupling - directed ortho-metalation